No because she's obviously an idiot and told him how it happened, now he can sue her. If she wanted to, she could have said nothing and gotten away with it. Was the satisfaction of his reaction worth the potential punishment? I think not. But then again, there's a reason OP named her a psycho.

To take somone to court, you need proof or the case will just be thrown out and op would be paying the fees.

Nah, my mum's ex was an abusive asshole and I almost did this with his house key in a bad part of town. Unfortunately my mother is too nice for her own good and took the key away from me before I could do it.

They could have broken up that day for all we know! Plus, he might not have realised she was crazy until they broke up and he didn't think she'd pull crap like this?

OP wasn't loaning out keys. They were dating for long enough that he gave her a key to his apartment, since she WAS op's girlfriend at the time.