Personal theory about the shooter.
Nothing but theory, just what popped into my empty lil head.
She lived in Tennessee, which is not an area known for being progressive. Women are treated like second class citizens and not respected.
Girl doesn't want to be treated badly, but instead of moving to an area with more enlightened views, decides to wear a suit and use a boy's name.
Rednecks see right through the cosplay.
Trying to dress like a guy to get respect just leads to taunting and "Haw haw haw! Didja see that lil' gurl tryin' ta act like she's a man? Haw haw!"
Again, instead of moving away and starting fresh, she gets the idea to go out in a blaze of glory, so looks for potential targets. Intimidated by most areas, she picks something safe and familiar, a school she knows the layout of.
Crappy guns, likely because just like mechanics and contractors, gun dealers see women as idiots and will rip them off at every opportunity.
Audrey Hale was no criminal mastermind. Perhaps she was groomed into being a martyr for some cause, but I think at the heart of it all she was a derpy kid that couldn't/wouldn't/didn't get her life together.