My dad bought a house for my brother to live in and rents the other four rooms out. Because of this, my brother gets the biggest room (a repurposed den). He’s never once had a complaint about it from his roommates. I’m saying this because it’s a similar situation to you: you and your family contribute more to the household so you get first pick on the bedrooms.
Your roommate sounds like a brat so I would be a brat right back. Don’t clean anything you made a mess of, show her the breakdown of what co-signing means, how much the furniture costs (I’m assuming it was all an upfront payment that she couldn’t afford), and if she has a problem with SHARING A BATHROOM I hope she never gets married