I'm 30 now, and I can remember back in the day when my mom use to take me out front of the house and whip me with her 2" wide leather belt. In PUBLIC. Boy, if that didn't learn me, than nothing did. She only did that about 3 or 4 times.
Here in my home area, they take juvies over to the prison and give them a grand tour. It'* called the "Scared Straight Program" I been through it a couple of times.
Let the punks take her car again, call the cops and report it stolen. Have em sit in the clinker for a night. That might work.