There are several previous threads on this issue, so you might look back and find some helpful information. I would suggest you charge her by the hour at a rate that you are comfortable with, and then add on the actual cost of the additional materials you purchase, you can give her the receipt as backup. Maybe give her a range based on the time you expect, but not locking yourself in to a flat rate just incase you encounter problems for some reason. I would think $10-$15 per hour minimum, unless you just want to donate some of your time for a good friend. The last baby quilts I made took about 5-6 hours start to finish with simple straight line and wavy line quilting, including the binding. I wouldn't touch it for less than $50 per quilt plus cost of materials.