My mom was hit by an uninsured driver. What can she do to have her car fixed by the girl who hit her?

About a couple of months my mom was rear ended. There was very minor damage and no injurys at the time they exchanged info and the girl supplied her with insurance info, and asked since there was only minor damage that we do not go through them. Then next day my mom called her insurance co to place a claim. Apparently the girl's ins has termed. So calling the girl she said shes sorry and to give my mom's car to her boyfriend to take to a family member shop to get fixed right next to the border of San Diego and Mexico, I don't think so. She is now trying to make it my mom's fault for not giving her car away to a random stranger to fix. My mom has supplied her with a quote from a reputable body shop in our area and now she has yet to pay or return any phone calls. The paint is now starting to chip away on her bumper from the hit. What can I do as a loving daughter to get my mom's car fixed?