You sound like a good and supportive person. Good luck to your friend. I hope that, at some point, she won't have to live like that anymore.
For years, we've kept meds that might be of interest to my son in my room and the door is always locked. The irritating part is carrying keys around and having to lock and unlock the door, sometimes many times a day.
When he was under 18 and using and out of control, we couldn't kick him out of the house (against the law).