Definitely DO NOT GIVE IN.
You be straight up with her and tell her what the cost for materials, batting, thread and anything else would cost and how much you cost for labor and add the two and give her a total.
If she still tries to fume or make you feel bad just mentally say N-E-X-T while smiling at her and stating you cannot possibly do it for what she wants it and move on.
We discuss this issue here from time to time and concenus is you charge what you think you are worth per hour plus cost of materials, if you design it, delivering it, etc.