me and my roommates don't tell each other bc when we have people over they just stay in our own rooms but we also established early on we didn't need to tell each other things like that so maybe let her know the first time and ask if this is something she wants a heads up about for the future
if your bf goes to the same college and is just stopping by for like an evening or an afternoon then a text should suffice (don’t need to give a heads up far in advance) but if he’s like long distance , visiting you, and staying over for the night then YESS YOU ABSOLUTELY HAVE TO TELL HER