Happened to me too, however I wasn't stupid and realised from day one she was lying, just by the way she was going on about it. So I let her carry on for a bit, then just completely ignored her and she gave up. (Also helped that her best mate told me she was lying). Oh and did I mention I also found out she also did the same to her previous ex! Needless to say, I havn't spoke to her since, and don't intend to. Some women are a danger to society