I made the terrible mistake of co-signing a car loan for a friend. I am forced to pay her car insurance because she won't. My credit is affected because she doesn't make a payment until just before she is threatened with repossession. She refuses to sell the car. What can I do to get myself off this loan, besides paying it off? What are my chances of winning if I take her to court to force her to either sell the car or refinance on her own or with someone else?

No, sorry there is no way to force her to sell it. And no way to make her refiance it ( and who would with such bad credit, and they would not do it without you last time)

Your option is to go ahaead and just pay the payments when due, so they are not late.
But why are you paying the insurance? That is not your issue, let him drive without insurance and report him if you want.

But basically you are stuck, to pay for his car if he don't, that is what a co-signer is.