[Coffee.]

While sex is completely natural, what she is doing is inconsiderate. It's her house, but you also live there too and need to sleep. Just tell her that her and her boyfriend have been "loud in their room" (which could easily be conversation, sex, whatever) and keeping you awake. She'll get the drift. I don't think she'll be angry; embarrassed, if anything, but she shouldn't get angry at you for having needs...aka, sleeping.