Maybe he's confusing you with someone else? Maybe go by his house and see if you see any vehicles similar to yours and then contact his friends on facebook to see if they've had any contact with someone pretending to be you.
No. Just no. She needs to stay the hell away from him, period.
As far as lawyers, sounds like this is more of a civil case than a criminal case so I highly doubt any real "charges" are coming her way. It would completely fuck over the ex-friend that co-signed for the car unless she can continue paying the note all by herself.
My true advice would be to keep doing what you are supposed to do, keep away from the shitbags, pay your car note as planned and make them come after you. The burden of proof is entirely on them not you. Document every single interaction you have with them and try to document all of your previous interactions. That's about all you can do.