Sounds like she was part of the gun culture (which is good), but being so, should also have known that most all mass gun murders that have happened in the last 25 or so years have a connection to psychotropic drugs — Prozac, Zanax, etc. She should have been more careful if her kid was on these types of drugs.
Exactly if she knew he had mental problems she should have never let him near her guns or take him to the shooting range. Instead she should have taken him to get help instead. Also if he was on meds and she knew it more so to keep him away from that.