you need to really look it over and figure out what it is going to take- write up a "plan of action"- including if you will be purchasing new fabric, batting, backing or anything else- such as fusable webbing...
do you have to re-quilt it? or pay someone to quilt it? machine or hand?
estimate the amount of time each step will take- then decide what you think will be fair to you for all your work and her--
i have restored baby quilts for $75, i have restored larger quilts for alot more- and a couple for alot less- you have to first have a plan in order to have any idea what the cost will be- i always tell people that is the only way to determine if it's fixable and what it will cost-and i try to guestimate a bit on the high side so they are happy when i can give them a little discount (like finding new batting/backing on sale-using a coupon)