head trauma to me.

Seriously, it doesn't take much, and it isn't always physically obvious.

Her head doesn't even have to have hit anything, a hard shake can cause brain injury.

Yeah, maybe she was high and that's what caused the accident, but it sounds like her behavior got weird after the accident, and an accident tends to be a buzzkill.

So, not to be diagnosing without a doctor license, but I'd STRONGLY recommend getting that woman's head examined right away, and not by a shrink.