Roommate Refused to Pay Bills

My question involves landlord-tenant law in the State of: Washington

I just recently moved in with my girlfriend(known as Stacy) into a house in which she is renting with another woman(to be Cathy). The lease was up at my apt buildig and Cathy suggested that I move in with them. Stacy, my gf, thought it was a wonderful idea as Cathy (let me reiterate, this was Cathy's idea) said she would move out, nbut to give her a month or so to find a place to live.

So, Cathy is supposed to be moing out on or before October 1 as Stacy and I just signed a new lease with the landlord starting on that date. Today, Cathy called the power co telling them she had moved out on Aug 17, which is not true in the least, and which is also the last day of the last billing cycle. Stacy told the power co that no this is indeed not true. Cathy then sent Stacy a text message that said (paraphrased) "we need to talk about the bills. I am never there and I will NOT be paying my 3rd."

Just was wondering how I should go about dealing with this. The bills are in Cathy's name, btw.

You will need to make sure that the utilities are transferred into the name of a current tenant, as I doubt that Cathy will be paying your bills. I cannot promise you that she has paid the last month's bill; you will have to check with the power company to determine if she has done so and, if not, whether they would let you move the utilities to her name and continue them without her (or your) paying that bill.

If you believe Cathy owes you money, you have the right to try to prove the validity of your claim in small claims court.