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Your resolution here is to sue your friend for breach of contract.
Depending on how much she owes you, you may be able to sue her in small claims court (both CA and NV have jurisdictional limits of $10,000.00). If the amount owed is greater than this, you must sue in general civil court (where the procedure is more complex and takes longer (assuming she actually appears in court and tries to defend the action).
As part of your lawsuit, you can ask for both money damages, and "declaratory relief" - ask that the court issue an order returning the vehicle to you.
Until you get the court order requiring the vehicle to be returned you are not going to be able to force her to give it back (repo companies cannot enforce your side contract).
Short of filing a lawsuit, you can try to mediate the dispute with them - contact your local bar association and request referrals to mediators, a third party neutral can often help you reach a mutually agreeable resolution. Use the bar association's referrals to contact a mediator or two, the mediator will then contact the other party to set up a mediation session, and you can go from there - hopefully resulting in a formal or written settlement agreement, and save yourself the time and expense of litigation.
I don't think that is what I said.
You can sue the friend for breach of contract. She is in violation of that contract, and she owes you the money.