My son was driving in the carpool lane with cruise control set to 70m/h? The other driver was in the lane to his right, driving

My son was driving in the carpool lane with cruise control set on 70 m/h. The other driver was in the lane to his right, driving 55 m/h. Then she suddenly tried to merge into his lane (carpool lane, and she was alone in the car!) and he hit her. Police report states that she was at fault and she caused the accident with unsafe lane change. My son's car was totaled. We only have liability insurance. Now her insurance informed me that because he was 5 miles over the speed limit, the accident is partially his fault. My son is going to college in 3 days and has no car now, he also left his summer job and lost 4 weeks of wages because of the accident. Can we do something and fight the insurance(AAA)?