Can I ask a cosigner that has a vehicle which I am the primary borrower to hand it over?

I recently found out that she is approx. 4,000.00 behind on payments. I just recently found out about it after receiving mail from lender. I asked her about it and she said she had it covered, wrong. I have the repo man hounding me. I contacted the lender and explained. I want to make payments and regain control of vehicle but she refuses to hand over the keys and now is parking the vehicle in undisclosed location. Can I have police assist me with obtaining the vehicle. I tried just asking but won't cooperate.