The guy crashed into my mother and he is sueing her?

I'm new to this sub but for obvious reasons , I am here. So about a year ago, my mother was trying to save up some money to afford a house so she started working for uber and lyft. While she was out late in the a.m.s , she parked to drop off a passenger and got hit from behind by a truck and slid a few meters. It was a really bad hit. The guy got out of his car and rushed to check on my mom and started rambling. He was saying stuff like "I'm sorry , i dropped my phone and was trying to get it , I'm late for work, blah blah blah" . Our car didn't work at all, it got junked. My mom's back hasn't been the same but you know how health insurance is so she is kinda stuck with it. She never tried to sue him or anything but now he's sueing my mom for a whole damn list of reasons. I am looking for advice. What are we supposed to do?