Illegal U-turn on red light

[chris92069]

California
-My wife was in the left hand turn lane in which a green arrow is needed to proceed behind a railroad crossing white lines.
-The other car was in the lane to her right. This lane is for straight crossing of the intersection, no turning is allowed from this lane. The car was also across the white line on the otherside of the railroad crossing.
-My wife had a green arrow and started to make her left hand turn. The car to her right that was in the staright crossing lane had a red light and tried to make a U-turn from that middle lane.
-The car from the middle lane hit my wife's car and caused $1700 in damage.
-The guy who hit her accepted full responsibility at the scene and gave her all of his insurance info
-Two people witnessed this accident and gave my wife their information.
-The adjustor from this guy's insurance company told my wife she was 10% at fault due to comparative negligence.
-How can this be she had the right of way with the green light and the other car tried to make an illegal U-turn on a red light from the wrong lane.
-The damage on her car is on the front fender and driver door so she could not have seen him comming.
-we have contacted our insurance company and as of today she going to make a statement.

*What is our next step? let the insurance comanys handle it? or samll claims court? we don't want any extra money we just want them to pay for the damage he caused.