Rehome my pet rat or buy new companions?

One of my rats has recently died, leaving me with her sister Moon (1 year old). I’m unsure what to do next. My original plan was to add two baby rats to the family, but I don’t know if she would prefer adult company/ an already established group. There are no adult rats available close by. Another conundrum that I’m having is that I’m in student halls and shouldn’t have pets at all (I brought them because I’d bought them previous my mum couldn’t handle them). The chances of anyone finding out are slim but I don’t know if it’s unfair to have rats like this. I let Moon free roam the room all day however. I put her on a pet adopting page to see if anyone would be interested, and a girl has messaged me saying she already has two rats and would like Moon to join the group. I don’t want to give Moon away but I don’t know what would make her the happiest. I also don’t know the girl who wants her and not sure if she could put Moon in harms way. Can anyone impart some advice? Should I get two baby rats or give her up for adoption?