My sister took her car to the mechanic to fix And after paying $900 for the work she drove the car for 10 min and the car burn on fire what she can do

My sister took the car to the mechanic to fix the car spares, the shocks, the tires and I oil change all job done on the same day. All done in license official mechanical shop she pays $900 for the job and after driving her car for 10 minutes to my mom house and park in front of my moms the car set on fire with her and the kids inside she didn’t notice until the kids neighbors tell her so she gets out scare take the kids out and the neighbors call 911,she called the mechanic and he came over he didn’t do anything about it now he’s trying to give my sister a older car that is broken down and he got offering to fix (mining he said he fix my sister car and the car got on fire) and the owner of the shop didn’t say anything about it yet it’s been a week since the incident and he has done nothing but just offer my sister a car damage and oldest car than hers. We still waiting for the report what can we do about it? We have all the photos of the car all burn.