I think it might not be on purpose. She probably just got busy and forgot. I would leave it if I was OK with loosing the fabric/ money but then I hate confronting. If not I would ask for the pieces back that she did not use and and also ask her to pay for what she did decide on to use. Just call her and kindly remind her.
I do agree that how it all went probably contributed to her taking it without paying for it. I tend to end up with situations because I am not clear or let people walk off with stuff.