Where can I get a letter to absolve my lease? Can someone post a link?

I live in a 3 bedroom apt and one roommate is making life hell for the other 2 of us. She has gotten posessive over personal and shared property and has sabotaged things in the apartment that could harm us (like the shower floor). We need to get out! We have approached the landlord and he won't let us out without her signed consent unless we take legal action. We just want to get out and never look back, we don't want to file a court case. Help!