1.Your guesses of argument that are likely to be put by her in the event of you taking up this matter legally, is just nothing but your wild imaginations.
First of all file a case as is required by law for getting the relief.
Without filing a case or even initiating any legal course of action why do you want to jump into such conclusions that she may try to defend herself with the contents what you have mentioned in your question.
2. You should not be bothered about what she may claim during trial proceedings before the court, let she come out with her own story, you can plan own strategies to confront them also accordingly. Without having agreed for entrusting the job and having acknowledged the work/task so far completed by you, she is not a mentally affected person to issue you a cheque without any reason.
You can challenge her during trial proceedings as and when an event/ challenge arises.
Discus with your advocate at length before initiating any action.