there's no formula here. you have to decide how/what/if you want to charge her. do you want to give it as a gift? does she really think you'll charge her anything, or is she expecting you to offer it? what kind of relationship do you have with her? if you want to give it but can't afford to right now and you have a good relationship with her, ask her if she can cover the cost of the materials used. if she's a good person, she'll at least do that.
personally, i think that what you charge an outsider depends more on the hours of labor than the cost of materials. if you do a whole-cloth quilt, would you charge for cost of materials? you'd be cheating yourself. you made an intricate, time-consuming quilt that will now be handquilted and the worth of your hours of labor will far exceed your costs for materials, unless you're working for $1 an hour. what does a salesgirl make an hour in your area? are you willing to earn less for what you do? and she gets benefits.
and yes. it's worth $600.00.