My favorite theory right now involves gangland drug-trafficking enforcers settling a debt and sending a message. The FBI will be all over that; there was a similar case last year in Upstate SC.
Because of Websleuth's restrictions regarding victimology, I'll keep my reasoning to myself. But I don't think this was totally random, and I don't think it was a love-triangle situation or a hate crime. I didn't see anything inappropriate about her partner's affect in her interview.
I do wonder if Katie was related to Marc Janness, a convicted murderer from Michigan. It's strange how little of a footprint these folks had online, apart from her SoundCloud
Katie Janness .