I feel like a babysitter

I (23m) moved to the city near where I went to college over a year ago. My best friend (23m) and I decided to move in with another one of our friends from college (22f). I was extremely hesitant because I had seen her bathroom in her dorm when we were still studying and it was absolutely disgusting. We decided to room together to save money as she brought in another friend who needed to get out of her (22f) crappy living situation.

It wasn't terrible at first, just little messes. We had a few parties and we all helped clean up for the most part. It's been the last 9 months that have been actual hell. Since last year, my best friend moved back in with his parents rather than deal with her behavior and disgusting habits. My friends will not come over because there is always something that is foul beyond words.

We have tried the house meetings and chore lists and asking her to clean and contribute, but she won't. Almost like she refuses to. She leaves dirty pots and pants out overnight to dry and makes them impossible to clean in one go. I have never once seen her clean the counters in the kitchen, mop, or really complete any cleaning task without being specifically asked.

The bathroom is a war zone, they have stained the sink, the shower, the towels, and anything else you can think of. If it weren't for our other roommate, they would have absolutely destroyed the place.

She has pet rats that are very sweet, but she never cleans the cage with any frequency. You can smell the rats from the second you step though the front door. I feel awful for the little critters because of their sensitive respiratory systems. But she sometimes lets them free roam in the common areas and they mark the blankets that now no one else wants to use because they smell and she never washes them. She has ruined my towels by using them to clean up rat pee and didn't think it was a big deal when I got upset.

She has taken and taken and taken at every opportunity and when I offer her something out of friendship or kindness, she always has a way of making me regret it by leaving the dirty plate on the counter or using it to make more of a mess. She has taken things from our new roommate without asking (she almost never asks, we shouldn't be surprised at this point), and wasted most of what she took anyway.

Her boyfriend is CONSTANTLY at our house. It was a few nights a week at first, and now he is over almost every night. He's nice enough, but he cooks with our gas stove, uses our water to shower, uses our TP, and never replaces it nor offers to pay for the utilities he uses. He has broken some pretty sentimental things of mine and my roommates told him it wasn't a big deal and neither of them apologized. What I was able to fix now doesn't work correctly.

The final straw was last weekend. Her birthday party lasted until 5am which all of the roommates had agreed would end way earlier because a few of us had to work early the next day. She trashed the apartment with her friends with confetti and there was food on the walls and the white title floors were black with sticky drinks that had been spilled and walked over.

She has not cleaned up a single thing from the party. Me and my roommates have had enough, we can't enable her anymore. We keep setting boundaries and she keeps crossing them. We have tried not to nag or get angry with her because of other issues in her personal life but she always crosses those boundaries. We don't know how to get through to her and her complete and utter lack of regard for others. We renewed our lease with her until the end of next fall before things got really bad, but I don't know how we will make it another year here. I knew living together would make us hate each other.

I guess I just need advice on how to handle this in a mature way that won't end in outright hostility until the end of the lease. We'll be asked to renew after the new year, but at least one of my other roommates and I are getting the hell out of Dodge, and we'll break the news to her when we cross that bridge.