I am a freshman female at my university - in my second semester.
I live in a triple dorm room; that is, I have two other female roommates J and P.
In the beginning of the year it was a bit awkward, as expected, getting used to living with each other. Neither of them had ever lived in a shared room before and were now moving into a small space that needed to be shared with two other people.
I am a generally clean person; I make my bed every morning, I don’t leave things on the bathroom counter, I put my dirty clothes in a hamper and do laundry every other week.
J is clean for the most part. She makes her bed and picks up her clothes but leaves half-eaten food out on her desk for days at a time.
P is verging on disgusting. She never makes her bed or washes her sheets, she goes a month without doing her laundry, she leaves her things (dirty clothes, bags, clean clothes, workout gear, packages, school supplies, etc) strewn about the room making it impossible to navigate without stepping on them.
I am not an extreme partier, nor am I one to stay in every weekend. I go out often with friends, always returning at a reasonable hour on weekdays and around 2 am on weekends. I make sure that before I go out, I set out pajamas and makeup wipes so that I can just slip quietly into bed.
J is a homebody, she never goes out late and is always in bed before midnight.
P is an extreme partier. About a month after we had moved in together, I received a call from the campus police saying that they had found her outside our residence hall, extremely drunk (she is 5’, 96 lbs, and had taken 12 shots). She was writhing on the concrete in her own vomit, after punching a girl and breaking her nose. Instead of transporting her to a hospital or police station, they put her in her bed (which is lofted about 3.5 feet) and asked me to come back to our room to take care of her. When I returned home, she had fallen off her bed and was unresponsive, and was in a pool of vomit. I called campus police to see if she could be taken to the hospital, but when they woke her up she became belligerent with me, punching me and dislocating her own shoulder. Campus Police left her in my care.
I generally go to bed by midnight on weekdays and wake up at 8 am. If either of my roommates are still sleeping, I leave the lights off and make sure to be quiet.
J does the same as I do.
P, at night, plays music on her computer without headphones, talks on the phone or on FaceTime, and invites people in while J and I are trying to sleep. In the morning, she sets her alarm for 6am, and presses snooze until my alarm rings at 8. This means that J and I are woken up every 8 minutes for 2 hours. IF P gets up before J or I do, she slams her wardrobe doors and dresser drawers, tosses her keys and bags, and plays music loudly.
P will let her trash can overflow for two weeks at a time before taking it out, leaving a smell in the room that makes people not want to come in.
I have caught P going through my things and taking them without asking.
Every time I ask P to be quiet, to pick up after herself, or to in any way contribute to the living environment, she responds with “You’re not my mom” or will agree but not do what I’ve asked.
I have gone to my RA and they say they can’t do anything about it.
I am going away for the weekend and I am afraid that she will “borrow” some of my stuff without asking or host someone in my bed.
What can I do to prevent this and to possibly fix her behavior to make the rest of the school year endurable?
Ear plugs for sound.
Sleep mask for when they won’t turn out the lights.
Advil PM for just plain getting asleep.
The library for not being in the same room as them.
Renter’s insurance for whatever get’s stolen or broken or go’s missing.
Ironically I’m describing the precautions I took against my older brother until he left for college and which he (ironically) employed against his terrible room-mates while he was there. Okay, not the renter’s insurance, that was just my brother. He got it for $40/year through our parent’s car insurance and he used it when his laptop “went missing” after his room-mate “left the door unlocked”.
My room-mate was a decent brother and my brother was a terrible room-mate and I’m really, really serious about the ear plugs, sleep masks and Advil PM. Admittedly this was all our mom’s way of getting us to not kill each other but it certainly worked and we’re both here today and I can’t help but laugh every time I think of my brother’s terrible room-mates and the righteous karma that brought that about 
Other than that, wait it out and actively pursue new and improved room-mates.
You can talk to the housing office and see if there are any openings in other rooms. Sometimes people go abroad in spring (more than the fall, usually), and space can open up. They may allow you to transfer rooms.
Also, have you talked to your other roommate about this? Is she on the same page as you are? If so, the two of you should go together to your RA and ask the RA to please help you, and if the RA is no help, go over their head to the CA (usually the RAs have another level above them). You should clarify for the RA that you don’t feel like you can keep your roommate safe when she has been drinking, you don’t think you should have to clean up after her when she does and makes a mess, and that she has been going through your stuff. The other stuff about messiness and being inconsiderate… well, I don’t know what an RA can do, unless they can help you with some kind of “roommate contract” and figure out how to help keep it enforced.
Is throwing an intoxicated student in her bed standard procedure for campus police?
I had two roommates in college, but we all got along. IF I’d had a roommate like you’re describing, there would have been an all out war.
If she’d left her stuff out, I’d put it in a bag and throw it in the hallway.
If her alarm keeps going off, I would have cut the cord with a pair of scissors.
Call 911 when she is in the state described above-that’s just plain not ok for you to accept the liability of her trying to off herself with alcohol.
Hide her phone.
Break her computer’s speakers.
Take her closet door off the hinges.
You see what I’m getting at here? You’re allowing her to walk all over you and treat you like crap. Time to start making her life more difficult than she’s making yours.
Hypothetically, of course. This is all what I would have done, I’m not recommending you do this. It speaks more to who has the power in your roommate relationship, and how to shift your thinking to get it back. What you choose to do to get it back is up to you.
You have to be super careful when you choose roommate…they may annoy your for a whole year.
This is why I want to live alone