My 15 yr old granddaughter was recently involved in a car accident that left one minor severely injured.?

She was underage driving. She was not drinking however, the other three minors in the car, and one adult were all drinking. My grandaughter thought she was being responsible by taking all the intoxocated people home. On the way home, she hit a soft spot in a dirt road, and one of the minors broke his arm. Now I, as the legal custodian, am being sued by the boys parents. They want us to pay for the medical expenses. What should I do