I don’t think we need her personality prior to the incident. Dropping this could save you some words and give the line more pace. If she has to kill to survive, and survival is her aim. State that clearly and I think you’re on a winner.

As an example.

A research assistant is trap underground after a contamination system locks. The leaked gas has produced psychopathic behaviour in her co-workers. She must now fight for her life while trying to escape this subterranean (prison). Prison is the wrong word. You know your story, so you know the best beats to add in. If you have a time pressure to add, even better. So after “Prison” you could add “before….”. So “before the facility is sealed forever” adds even more stakes and more pace.

I like these types of stories, good luck.