I agree with Matchka, but…
Did your Mom back into the other car? Or did the other car hit her in the side when she backed out?
If your mom backed into the side of the other car, then it is her fault.
If the other car backed into the side of your Moms car, while going in reverse, I would say it is there fault.
IANAL, but in general, a vehicle operator moving in reverse is required to exercise special care. In this case, both operators were, but your wife was performing a normal operation of parking, and the other driver was not. The situation is murky, and subject to the vagaries of local and state law, but as a general principle, the vehicle which strikes the other one (with its rear bumper) is more likely to be considered more at fail if the case is tried (barring other circumstances), though a weaselly finding of 50-50 responsibility is always possible.
Think of it this way: you are entitled to occupy whatever location you occupy (if you got there legally, as it appears both did) but no other vehicle is entitled to hit you. The car that was struck on the side was in place first - or more accurately, if the car that was struck on the side had haltyed one second earlier, it would have still been struck, just in a slightly different spot (assuming low speeds for both parties) yet if the other car, striking with its bumper, had stopped one second earlier, the collesion would have been averted, regardless of the velocity of the other car. Hence the later car (striking the other with its bumper) would seem to be more proximately liable.
I believe, in most jurisdictions, doing something illegal can tilt the scales against you.
Years ago, a girl I was dating exited her dorm and found a policeman near her car writing a report. It seems that a women has struck her parked car 3 times while trying to exit a parking space. My girlfriend, the owner of the parked car, was charged with the accident because she was in a “No Parking” zone. The woman had PLENTY of room to get out of her space safely, but the accident would not have happened had my girlfriend not broken the law.
Again, it depends on the jurisdiction, but I have lived in places where driving against the directional arrows constituted driving the wrong way on a one way street. If there is any financial advantage, it might be worth fighting liability.
I live in Michigan, a no fault state. If I am in an accident where I am not at fault, I don’t have to pay my deductable. Also, my rates don’t go up if I am not at fault. So, no fault doesn’t mean no fault.