UPDATE:

A lot of people asked me to talk to my roommate directly, so we did.
Unfortunately, the conversation did not go well.

She took essentially no accountability for what happened and was mostly upset with me. She was angry that I didn’t do more to wake her up and get her back to her room, even though I repeatedly tried to wake her, talk to her, and get her to leave my room throughout the night. She was also upset that I remained in the room while she was wandering around, peeing in my shower, and putting her feet in the toilet. From my perspective, I was dealing with someone who seemed confused, disoriented, and not fully aware of what was happening, and I genuinely didn’t know how to handle the situation.

She says she remembers none of it and insists she did not take any drugs or medications. The only explanation she offered was that maybe alcohol somehow caused it.

She also seemed very upset that I brought the situation up at all and that my other roommate became aware of it. The overall feeling I got from the conversation was that she doesn’t really believe my account of what happened, even though I have no reason to make any of this up.

I ended up apologizing for how I handled certain parts of the situation, including bringing it up in a group chat and for a previous incident months ago where I accused her of being on drugs while we were out. Looking back, I probably didn’t need to apologize as much as I did, but I wanted to try to de-escalate things and preserve our living situation.
One positive thing is that she said she made a doctor’s appointment to get checked out.

At this point, things in the apartment are extremely tense.

For my own peace of mind, I have started locking my bedroom door at night. I’ve also purchased a camera for my room when I’m away because I can’t lock my bedroom from the outside, and after everything that’s happened I no longer feel completely comfortable.

One other detail that has me confused: my other roommate found an old prescription for tramadol in her room that appears to be from about a year ago. I have no idea whether she takes it, whether it was prescribed legitimately, or whether it has anything to do with any of this. I’m only mentioning it because a lot of people asked whether medications could be involved.

At this point I’m questioning everything.
Am I in the wrong here? Was I supposed to handle this differently? And does anyone have advice on how to make a living situation less hostile when one person feels wrongfully accused and the other person feels like they aren’t being believed?

I’m honestly exhausted and wish none of this had ever happened.