meh, I say go for it if the roommates are cool with it. I’ve stayed at my girlfriend’s dorm for 2 weeks. It was a shared room and I was good friends with her roommate (who was cool with it). I’m sure there were rules against extended visits, but the RAs were very lax and didn’t enforce them much (unless the roommate complains). Just learn how the dorm operates so you can navigate without getting anyone into trouble. My gf or her roommate had to swipe me in every time I entered the building past 9pm, and the guys living in the male hall gave me the code to their bathroom.
Just stay in an airbnb somewhat near her. Philly is a nice city, I’m assuming she lives on campus in University City?