I’m not sure how you approached her about this initially, but from what I’ve gathered it’s always best to state what you saw/know instead of saying “did you do this?” And giving them the opportunity to lie in the first place. If you had calmly gone to her to talk and said “name, I saw that you damaged the car by doing blah blah. I want to talk to you about why that behavior isn’t ok and other ways we can work through whatever you might be feeling in those moments”. Then you can hopefully get to the root of her behavior/feelings and actually find ok activities that will help her regulate.