My sister and I had a contract that started she would take over the payments for my vehicle, she has paid for 2 years now decided she no longer wants

Yes, but it may have to be in writing, since contracts that cannot fully be performed in one year are required to be in writing.  Also, if you donlt hae it in writing, there is no guarantee that the court will believe your story rather than your sister's who may claim, for example, that she agreed only to make payments on the car so long as she used it.