Death of co-signer

My sister signed on a contract with me for a vehicle so I could get a better interest rate. We both understood that her only connection to the vehicle was her name on the contract. She recently passed away and our brother, who is the executor of her "estate", wants to tell the credit union of her passing to get her name off the contract. I think that the only way that will happen is if they rewrite the contract in my name only, and with my credit score. That will make my interst rate quite a bit higher since I am credit challenged. I realize that is my problem that I created, but she would have preferred that it be left alone. She had no qualms co-signing the contract to help me out. Is there a law regarding this issue?

Check the loan docs but he does not have to report a co-sign by law normally...the docs may require it however...