Well , I am inclined to think that since she is aware of the cost of materials to be used in making a quilt and your time in making it special, she took advantage of you. She should of said how much she was able to pay before the project started and that would of given you the option to say... yes or to have just presented as a gift!
Her asking for additional quilts made the same, for the same, is out of the question. You should just tell her you cannot do it for the same price and give her a figure of what you would charge for the others....