As an RA Ruth cannot catch everything, as a resident Mary should have reported any illegal activity. Also I am not sure what Ruth would get in trouble with when it comes to having Billie over. Alcohol maybe if they caught it on her, otherwise its Mary's word against Ruth's.
This. I'm not too familiar with the way these things work, but I would think the residence manager would take Ruth's word over Mary's, unless of course, Ruth and her hall has a publicly-known history of rule-breaking. It
would put Ruth under a magnifying glass, which would lead to discipline unless she changes her alcoholic ways, which we know she's not likely to do.
As to Ruth 'fraternizing' with Billie, that actually
could be against the rules, considering their relative positions of power. Power-imbalance in relationships can lead to favorable treatment in otherwise unrelated situations. It would be similar to the rules against professors dating students, though in a dorm it would be about the RA's significant other getting away with rule-breaking, as opposed to wrong answers.
Totally right on the RA not being able to catch everything. I've actually been in a very similar situation to what's happening in the comic with Becky, though I was playing more the parts of her friends. One of my semesters in college, I had no roommate. Not officially, anyway, but it happened that a good friend of mine that same semester got kicked out of his room for his grades. So, in all actuality, I had a roommate. He
did, eventually, have to move out, but it was because they banned him from the dorms entirely, even for social situations, not because they found out he was squatting in my room.
