I'm not sure Eliza is capable of [i]killing[/i] somebody. At least, not yet.

But having Alice as a roommate is gonna change Eliza's approach substantially. She isn't going to try to provoke conflict with somebody she has to live with. I mean, would you?

The way I would see that going is honestly pretty straightforward: Eliza tries to be nice to Alice, at least tolerably so, Alice rebukes her completely and does drugs and shit in the room, Eliza calls the police, and gets a new roommate. I dunno if that's the drama we were looking for...

I say, if Alice is to be the villain of this part of the plot (if Acacia is the hero, and Eliza is the anti-hero, and I'm only putting it in those terms for convenience, not to put anybody else's characters on the sidelines), let her be the villain. She should have time to scheme and plot and come into her own in that way. The bigger they are, the harder they fall.