Legal question about suing?

I live in Montana. One roommate is trying to keep the deposit from my other roommate and myself, so I have been refusing to pay the electric bill or carpet cleaning, due to the fact that it will/can come out of our deposit. I don't mind having lessened the deposit since I won't see any of it back anyway. Can she sue me for not paying 1/3 of an electric bill if I have never signed anything with the electric company and the bill is in her name? Also, my 3rd would only be $43, is there anyway that she can even take me to small claims court for a sum that small? I have tried to type up an accord for us saying that I agree to pay my 3rd of everything if she agrees to give me my part of the deposit minus any damages, but she won't agree to that. What action should I take, if any?