When you come up with a reasonable value for the car, I would suggest you send a demand letter asking her to compensate you for the value of the vehicle before you go file a claim with the court.
I would also include the proof of it's value or how you arrived at it anyway.
Give her the chance to pay you first. It's doubtful that she will actually pay you, but you never know. If she agrees that she is responsible for the loss of the vehicle, see if you can come to an agreement on the amount of the loss and if she is willing to make payments. If so, draw up a contract with all the terms you agree to. Total amount, monthly payment amount, any late fees/interest and what date the debt should be paid off by. Get her to sign and date the agreement.
If she doesn't meet the terms of your agreement, then you can go to small claims and armed with the police report, signed note and the amount of money already paid, it will clearly show that she is responsible and has taken responsibility for the loss of the vehicle, making the judge's job easy and the case will be a fast one.
If she refuses to pay you anything then you can file the case against her. You might mention to her that if you have to go through the courts, she will have additional costs and the civil judgment can hurt her credit and have her looking irresponsible on background checks.
You should be willing to accept reasonable payments from her as the court Will find that monthly payments are acceptable should you prevail. So either way, I wouldn't be expecting one lump sum unless she has access to some deep pockets.
If you sue her in small claims don't be surprised if she counter sues you. This is pretty common, as many people believe a weak offense is a good defense.
