George,
Have a read thru some legal documents.
Im pretty sure due to that fact she hit ur bumper, regardless of the fact that it already had some stratches, she still has to pay to fix it. As you cant just spray one small spot of ur bumper to fix what she did, u have to spray all of it. Otherwise the colour wont match. The fact in doing so will fix the other stratches is besides the point.
I remember reading some about this in my legal studies, tho im not 100% sure. So have a chat with a few more "legal minded" people.
I dont think of it as being cheap, it was her fault for not putting her handbrake up, so she should pay for it. I would of done the same thing as u did.
Tell me one thing.... was she blonde?