Our D’s room contract also limited the number of overnight guests/term. That may be your “in” to try to discourage the visits. I’d also strongly encourage your D to get involved with a club activity on campus. Many times they meet on the weekends so she won’t be free to host the HS friend.
FWIW, I feel for you OP. My brother is going through something similar with his own daughter. It’s really put a damper on her making new friends at school her entire freshman year.
While I agree with the other posters that you have limited influence with a young adult, I would exert what pressure you can to encourage her to focus on getting integrated into her campus community before hosting this friend.