What are my rights as a co-signer HELP!?

i recently co-signed a vehicle for a friend. since the day i signed the papers it has been nothing but trouble. my now ex friend went to the same dealer i went to because it was the only place that would lease to her because she has such awful credit. she payed $15,000 down and payed 6 months of her insurance. now she has to pay the broker who helped get her the car and she refuses to. saying that i worked some sort of deal with the broker to get money out of her. which is compleatly untrue. now i have creditors calling me everyday about the money. i want nothing more than to get out of this lease. my ex friend has also been sending me threatening messages about paying her bill. this woman is a fool what can i do legally to stop this harrasment. she is ruining my perfect credit and i need help.