Beside what the others have said - risk being asked to leave, no ME, and no early/late hours - you will not be able to have her on the dining plan if you have it. If you are over room capacity, what exactly do you expect to do for her to sleep - not to mention being overcrowded. Sorry but its not worth all the trouble - I would just get a room to fit all of you or consider staying off-site if that is the only other option. If you end up taking her, make sure you have a copy of a medical insurance card and a notorized letter signed by her parents stating that you are allowed to make medical decision for her.