Hermione was able to go into boys' dorm. I remember her talking with Harry and Ron while sitting on one of the bed in Harry's room in Gryffindor Tower. On the other hand, stairs didn't allow Harry and Ron to go into girls' dorm. The reason given was: Boys aren't trustworthy.
But, if I was at Hogwarts, provided that I could fly on brooms, what could prevent me to go into girls' dorm? Was there any other magic in place?