In general and with some exceptions, I think this author is on to something. The one thing that would have stopped the Orlando shooting, maybe, is if he had been convicted of his domestic abuse. His wife might have come forward, or the FBI might have uncovered it during its two investigations of him. Either would have prohibited him from buying or possessing firearms under Federal law. He might have obtained guns illegally -- criminals usually skip legal gun sales entirely, and obtain guns from friends or family. But it's the only law-oriented suggestion I've seen that might have stopped him.
She's right that domestic violence is often (not always) tied to mass shootings, but even more, that it's often tied to later murder of the person being abused. She's also right that close family, the ones licensed by law to apply for restraining orders, often know well before anyone else that someone is likely to commit irrational violence. That adheres to my principle of thinking of citizens as performing that key militia function in the defense of the common good and lawful order. Just like the Rangers have peer reviews, sometimes citizens' militia members might need to say, "Not this guy, though -- he's going to kill somebody for no good reason." We can't make that a general power of citizens, because some would use it as a backdoor to disarming everyone. But it might make sense to do it in a way restricted to those most vulnerable to domestic violence, who are also therefore in the best place to know when someone is violent in this way.
There's room for something here that I think reasonable people could agree to doing, even if she hasn't got the specifics mapped out yet.