The bill so far is understood to be in the region of pounds 460,000. This includes pounds 60,000 for Barry Scheck, her defence attorney, who won fame for picking apart forensic evidence when he represented OJ Simpson. Another pounds 36,000 went in fees to six medical experts.
But the final cost could be much higher, especially if the Eappens sue EF Au Pair. A spokesman for the agency said: "Louise and her family have our full support. We firmly believe Louise is innocent."
Other au pair agencies are also bracing themselves for a backlash as the bad publicity surrounding Matthew Eappen's death slows the flow of applications to au pair programmes.
Sandra Landau, director of Childcare International, which sends au pairs to the States and receives them from Europe and Scandinavia, said the case had alarmed potential applicants.
Yet the American au pair system was much more tightly regulated than the British, through eight authorised agencies. Something was more likely to go wrong in Britain than in the States.
Mrs Landau said: "We have always been impressed by the care taken by the US immigration authorities over these applications. They are very strict. The girl has to come up with the necessary references."
By comparison, there were no checks made in Britain where there was only the security of working through a reputable agency, Mrs Landau said.
She defended the au pair system and pointed out that the Eappens could have chosen a fully qualified nanny. "We think it's a wonderful opportunity for any young person to have a carefully protected stay in the States. And, for American families, it's a guaranteed reliable service of childcare for a year."
The agency, Au Pair in America, said other factors, including fewer people taking gap years before university, were contributing to the slow-down in applications for posts in the US.
Sandrine Picquard, of Au Pair International, said demand for au pairs would continue, but the case might make people reflect more on what happens in Britain. "The net in America is very, very tight. Here, a lot of people don't want to pay an agency." She added: "I know people who have been in my business for 50 years and when I ask them how many horror stories like this they've heard, they say none."
Since Matthew Eappen's death, regulations in the States have been tightened further with the co-operation of agencies, including EF Au Pair. Au pairs taking care of children under the age of two must have at least 200 hours of childcare experience and undergo eight hours of safety training.
Yet, three years ago, parents had objected when the age of au pairs was raised to 21 and their pay increased.
Maureen Smith, of the Council for Awards in Children's Care and Education in Britain, said they always strongly recommended that a person looking after children should be qualified. "It's not an easy task."Reuse content