Something to mull over: If it is someone you know well or are concerned she won't want to or be able to pay more than what you would charge for the quilting, could you barter something for the time piecing and charge for the quilting?
I frequently barter or trade off. I feel badly asking someone to watch my kids but need to ask sometimes. I will trade off and watch theirs, make them food, make a table runner or baby quilt, babysit for them... I have even painted a bedroom for a friend who watched my kids a few times and I helped "unhoard" and organize for another friend.
Bartering is easier way to go if $$ makes you feel uncomfortable, especially b/c you didn't discuss the price in advance.
Hope that helps.