Call the police. That would be a crime and she could be facing some time in prison.

Time to go to the police and press charges, get a restraining order while you're there. People like her need to learn that they don't own their partners, and to ask about things. And also to keep their noses out of other people's business. This could have all been avoided if she'd simply asked, "Who is Kristi?" Not demanding, either, just ask. Unfortunately, this is what happens when there's no consequences at a young age. People grow up to act all sorts of stupid, and were never taught to talk about their problems instead. So instead of talking, they destroy stuff, only to find out that the Real World has consequences for that. Regardless, go call the police. Press charges. Possibly find a lawyer if you have money and want to make sure it's a lesson she'll never forget.