<human>: About a month ago I moved to San Francisco for school. I mostly share a (one) single room with 29M, then 19F and 20M join us in the same room on weekends. We have an un-used bunk for guests, and this is where the contention lies. 

There is a 18F who wants to move across the country and possibly room with us, rent free, for a month. For some reason all 3 of them seem to be on-board with this idea except for me. 20M assures us that although she doesn't have a job or much savings, she's a "really cool person". 

Am I just being an uptight asshole, or is this really as bad of an idea as I think it is?

Can you succinctly summarize the text in 1-3 sentences?
<bot>: Single room w/ bunk beds, roommates want to invite additional roommate to stay rent-free. I'm not on board with this idea, other roommates are. Am I being too uptight about this?