If you've read "Mistakes Were Made (but not by me)" you will understand that even a confession is not really reliable because of the way police interrogations work. Certainly changing the story - especially when being interrogated in a second language - is not unexpected. I'd be more suspicious if she had everything perfectly consistent from start to end, every single time she was asked. That would be evidence that she rehearsed the story too well.
(apologies for pimping one of my favorite books. . . again and again and again; it's just that good :)