I'm surprised this hasn't come up in the comments yet, but it sounds like she has severe PTSD.

This is how it manifests. The arousal level is set through the amygdala to "constant threat" and she goes into immediate fight mode.

I would recommend an assessment with a therapist.

Did she grow up in a home with constant danger or trauma? That's how it happens, usually. They call it Complex Trauma, because it wasn't one specific episode, but occurred over time. Maybe an alcoholic mom or dad.

At any rate, it's deadly. The suicide rate for people with Complex PTSD is very high compared to those with single episode PTSD.

It's not a mental health disorder. She may not have any mental health problems at all, but again, she might, but would need to see a therapist either way.