The first question to ask yourself is whether you want to make the quilt or not. If you do, you may be happy with a token payment, which is what I think the $50-75 would be. After all, that's probably less than a longarmer would charge to just quilt it with a simple allover design. If you don't want to make the quilt without being paid a reasonable hourly wage, then probably all you need to do is tell her how much fabrics cost and the offer will be withdrawn. If she still wants to go ahead with it, you should consider how much time it will take you and how much you want to charge per hour and present her with that charge for labor, explaining how you arrived at it.