In 1994, her sons Alexander and Constantin, then aged nine and seven, were abducted by their German father, although she had been awarded custody.
Over the next nine years, she saw them for only a few hours; her seemingly endless court applications achieved nothing and cost her all her money and peace of mind.
And even now that her sons are in their twenties and they have all, with some difficulty, re-established a relationship, she is unable to discuss what happened without her voice trembling. 'In those days, people were entirely unaware of parental abduction,' she says. 'They always assumed that I must have done something wrong or that my lawyer must have been an idiot. It was a very little thing to cope with on top of everything else, but it didn't help.'
We have met to talk about Parents & Abducted Children Together (PACT), the charity she launched in 1999 to help other parents in the same situation as herself, recruiting Hillary Clinton as honorary chair and Cherie Blair to launch it at the British Embassy in Washington.
This year, to mark International Missing Children's Day on 25 May, Lady Meyer filleted her address book and sent out cards in the shape of balloons for her celebrity friends to decorate.
Roger Moore, Whoopi Goldberg, Ralph Fiennes, Michael Caine and Robert Pattinson did their artistic best; David Cameron and Nick Clegg took time off from their political duties to draw for her, though, rather tellingly, Gordon Brown simply sent a Number 10 Biro.
When we met, Lady Meyer was still hoping to receive balloons from Clinton and Kofi Annan.
The results are being auctioned online over the coming week, and all the profits will go to PACT, which has expanded its remit to embrace all missing children, working with the police to rescue them and helping to counsel parents on their legal rights.
(She has been in contact with Kate McCann, for instance.) And it's a growing problem: PACT estimates that a child goes missing every five minutes in the UK alone – some run away, some are abducted by parents and a few are taken by strangers.
'Awareness is incredibly important for people when they get married,' she says. 'Say you go to Greece, fall in love with someone, get married and have children, and after two years you find that you don't enjoy living on a small island. If you come home with your child, that's abduction. It's illegal, and people don't know that.'
A lot of venerable institutions are in her firing line: the children's charities for their piecemeal approach and the courts for encouraging confrontation between parents, and for lack of awareness of international law. 'I get a lot of letters from parents about Germany – the German courts hide behind their constitution, and have this quite incredible belief that a child is always better off in Germany.
And here, in the High Court, a judgment was recently made based on the views of a five-year-old, which is absolute insanity. Asking a child to choose between its parents is really unfair and they don't understand the consequences of what they say. Judges have a lot to answer for,' she concludes bitterly.
Ironically, Lady Meyer was born in Germany. 'A complete coincidence,' she says. 'I'm definitely not German.' Her mother Olga is Russian-born but was brought up in China; her father, Maurice Laylle, who died recently, was a French naval officer who sub-sequently worked for Mobil.
Her parents moved to Africa, then settled in London when Catherine was 12 and sent her to the French Lycée – which is why she still has an unmistakable French accent.
Catherine graduated in Slavonic and East European studies at London University, then became a broker at Merrill Lynch.
When she was 29, on holiday in Brittany, she met Hans-Peter Volkmann, then a 27-year-old medical student.
A year after they met, they married in the Russian Orthodox Church, and their first son Alexander was born in 1985. He was only a few months old when Volkmann announced that they were moving to Germany; a month after Constantin was born, Volkmann decided to leave his job, and the family were reduced to living in one room in his brother's house until he found work again six months later. When he decided to leave another job, Catherine realised she no longer loved him.
The divorce was, as far as she thought, civilised.
They were legally separated in 1992 and the agreement was that the children would spend holidays with their father. It was after one of these visits, in August 1994, that she received a 21-page letter from her ex-husband refusing to return his sons. He claimed that they felt they were German and wanted to go to school in Germany. 'My whole world crumbled in an instant,' she recalls. 'I started to panic. I was phoning and phoning, and nobody was answering, and I didn't know where they were for weeks.
So my lawyer sent a fax saying Volkmann was in breach of the custody agreement and that we'd have to take legal proceedings if they weren't back when they were supposed to be. And they weren't.'
Why does she think he did it? 'A lot of people do it because of anger,' she says uncomfortably. 'It's a way to pay someone back. You know, "She left me, and she shouldn't have left me." In general, people don't behave like that for clever reasons. If you love your children in a deep, unselfish way, you know that they want their mummy and daddy.'
She kept her sons' rooms as they were for as long as she could. 'As a mother, you can't accept that you won't see your children again. I believed they would come back,' she says.
But the legal proceedings ate up all her money, she lost her job and had to sell her flat, her jewellery and her possessions.
Meanwhile, the children she fought so hard to keep were becoming hostile strangers.
She's reluctant to go into it all now because she has re-established contact with her sons – 'they get very embarrassed' – but when she saw Alexander for the first time and told him, 'I've been trying to see you. I love you,' he called her a liar. 'Papa told me that you could come and see us whenever you wanted and you never did.' On another occasion, when Meyer approached them at school, Alexander said, 'Our [paternal] grandmother told us if we ever see you we should run and scream.' And when she was eventually allowed to visit her sons, it was in a locked room with someone else present.
During her ten-year campaign to get her children back, she met Britain's new ambassador to Germany, Christopher Meyer, then separated from his first wife. 'There was a queue of women outside, all keen to meet the ambassador, but I was completely uninterested,' she recalls. 'The last thing on my mind was men and a relationship. As he says, "This poor mother came to see me and I wanted to help her but there was nothing else I could do, so I married her." That was the silver lining in the very black cloud,' she says, smiling affectionately.
They married a few months after they met, in 1997, because Sir Christopher had been appointed to Washington and had been advised that the strait-laced society there wouldn't accept him arriving with his girlfriend. 'I was a bit shell-shocked, and my father was completely worried about his vulnerable daughter and if I was doing the right thing.
I didn't know Christopher well and I didn't know what an ambassador's wife was supposed to be, but it was very exciting.' From a lonely existence she was catapulted, Cinderella-like, into a glamorous society where every evening took her to another party in another dress.
They had 14,000 people through their house every year. 'Every night, we were going out and meeting people and shaking hands.
We were there for Monica Lewinsky, the elections, the recounts, 9/11 which was indescribably awful, Saddam Hussein – it was an incredible time.'
Naturally, it didn't take long before her custody battle, which had been in the British press, made the newspapers in America. She began to receive letters from other parents in similar situations.
The letter that inspired her to found PACT came from an American father whose German wife had taken their children away on holiday and then announced that she wasn't coming back and he would never see them again.
Two years later, the ex-wife returned to the States, having put her children up for adoption. 'The children didn't even have German passports, and for two years they'd been living with strangers,' she says. 'He tracked the children down to a foster family and said he was coming to pick them up, and the foster family refused to give them up. That story really started my lobbying. He was all-American, in the army, he was just perfect, and that was what was happening to him.'
Campaigning also proved an emotional release for Lady Meyer. 'I could never relax on a beach, I could never have time out,' she says. 'Kate McCann is the same. As long as I was fighting, I was passing on the message to my children that I hadn't abandoned them.' And did they get it? 'They never found out. But they can now if they Google.' After six years in Washington, she and Sir Christopher came back to London. These days, she says, they hardly entertain at all. 'We're still digesting. I do miss it, but at the same time I don't. It was a chapter in my life. It was nice to be called Lady Meyer and have people opening doors, and my own car, but now I can go anywhere and people don't stop me.'
You sense also that now that she has re-established contact with her sons, part of her would like to move on from PACT, too. 'Christopher complains I'm a workaholic, mainly on PACT,' she says. 'I've been doing it for ten years and it so absorbs me, and I'm so passionate about it.
But I feel it would be nice to relax and do something else and not pick the scab all the time.' If she continues to campaign it's in the hope that she can prevent other parents and children going through what she and her sons have suffered.
'Everyone discusses money before they get married,' she says, 'but if you're marrying someone from a different nationality you need at least to think about what might happen to your children if you split up.
Pakistan and India are quite complicated countries, and if your child is abducted to Japan, it's bye-bye. My advice is to marry the boy next door.'
For more information on the PACT celebrity art auction and how you can help raise money for missing children in the UK, visit pact-online.org
