Watch the interview again... The reporter was trying to lead her to a different conclusion to what she was saying. He supposedly user and AR15, you cannot shove that down your pants.
The reason most conspiracy theories are discounted is they are so complicated.
Breaking the human psyche is a complicated process with no guaranty of the result.
If I was planing an attack of this nature I would just search social media to find a kid with issues, with the kind of psyche that would be excepted as a school shooter. Lure him one way or another to the location, do the deed and leave him to take the blame. Simple, clean and effective.