It sounds like the insurer of the vehicle that hit your mother'svehicle is saying this claim falls under a medical emergency and therefore has decided the insurance company is not responsible to reimburse you mom for her damages. Or it might be that the person did not let their insurance company know about their condition and so they were not covered due to the omission of this medical history to their insurance carrier.

If your mother has collision coverage on her vehicle she should check with your insurance agent to see if she can make a claim that way. Beyond that she might want to seek legal advice to see if you are able to go after the driver personally for your loss. To find out if you have any other rights or want to find out more about why the other party's insurance company would not cover this incident you or your mom can contact your state's insurance regulatory body.