The 2nd amendment starts with, " A well regulated militia...". If I am not mistaken the Supreme Court decided that owning a gun had nothing to do with a well regulated militia and more or less just ignored that part. I would not have ignored that . Own a gun - be trained in a militia much like the National Guard. Maybe a 10 year stint or lifetime or as long as you own a gun other than hunting or target.
Why did this mother of the shooter own an assault rifle? Are 3 weapons 2 too many? Was she part of a well regulated militia? She should have been.