Sorry to here whats happened, from a legal point of view stopping a cheque is only a criminal offence if she had no intention of paying, or had insufficient funds to honour the cheque.
so a tricky one to prove, but it would impossible for her to prove you did it, because you didn't.
it's just whether you want to pursue it, i would start by talking to her which i assume you have done already, them put it in writing denying any responsibilty, and giving her 14 days to meet payment, or be responsible for recovery costs on top of the amount due.
At this point you need to decide if you want to pursue further, if she has not already paid.
of course keep all corrospondence and remember what you say in writing may at a later date be scrutinised in court, so be seen to be fare and reasonable, judges dont like bloody mindedness, i dont suppose it will get that far though but worth remembering.
Good luck
shame you did not have your camera with you, a photo at the time would be handy could have used your mobile
