I would tell her (via e-mail so you have a copy) that she owes you the agreed upon price, NO DISCOUNT and if at the end of one week she has not made a payment or paid in full, it will go up for sale for $300 and if she wants it after the week is up she will have to pay the $300 in full. If she wants the material back, give her any scraps and tell her as she went back on agreed upon contract, she is out of luck, but she can have what is left over. If she doesn't like it tell her too bad, you broke contract so your just out of luck. Stand tough because it sounds like she pulls this on other people as well.