Now for the tough questions... If the mother had a develpmentally challenged and/or emotionally unstable son (rather he lived with her or not) why didn't she secure her firearms properly. Yes, that means she bears some responsibility for what happened.
If there is room for new laws, thats were they are needed... Laws to hold gun owners responsible who are careless with their proper storage. ( I know shes dead... But the law would have prompted her to lock them up properly to begin with).
Had she had a proper gun safe, and proper control of access to said safe, they could not have been stolen and used by someone who orherwise would not have had access to guns... Yes, the son tried to legally purchase his own gun the week before... And properly was denied due to a history of mental problems.
Additionally... Consider making it a crime even to try to buy a gun if you are inelligible to actually buy one... Then maybe authorities could have arrested him at the attempt time... At least detain him long enough to determine if he is a danger before releasing him again. This approach would leave legal law abiding citizens alone, but allow immediate examination of an unlawful attempt.