Even if the police didn't charge the driver, it would not stop you from sueing the driver.
Here are several pieces of information you might want to gather:
1) If the police issued any ticket to the driver or not
2) If there is any police report or not, and what the police report says
3) If you mom's auto insurance company covers her bodily harm injury or not, when she is involved in an accident as a pedestrian.
4) If your mom was sent to hospital or not, right after the collision and what the medical record and diagnosis.
5) Check to see if there is any survillance camera around the parking lot and if any video was taken for the scene of accident.
6) Try get the previous driving record of that driver to see if he/she is proned to be a reckless driver
If your mom was hurt, by all means you should try sue the driver.
If the driver's insurance company's designated regional agent didn't contact you after a few days, seek an attorney and vindicate you and your mom in a merciless way.
If the insurance company's agent contact you and try to settle the case by offering you a peanut which is about the same as the medical cost, refuse it and file the suit.
The attorney fee better be arranged as contingent payment---no compensation or reward, no payment of legal fees. 1/3 of the law suit proceeding should be reasonable.