It's important to remember that finding drug paraphenalia is not the same as finding someone shooting up. Yes, it may be illegal to have illegal drug use going on in the unit, but at this stage of the game you cannot and should not assume anything. There may be signs of drug activity but you have not proven anything and, in my opinion, there is not enough evidence to give a 3-Day notice to evict. This is why it is vital to connect with law enforcement and get their further direction. Oftentimes, an Officer can accompany a Manager at some random time and "catch" what is going on in the unit. Trust me on this one. Drug users can be stupid enough to leave their bags out in plain sight - even on a window sill! for all the world to see, which will absolutely produce probable cause for entry.
Secondly, Sandy, you can send a letter to the Resident about the fact that you suspect someone is living with the Resident: mattress on the floor in second bedroom, etc. But this would not be a 3-Day Notice, rather a 10-Day or whatever your state allows. Then it is of course up to the Resident to decide what to do: come in and talk to you about it or kick the person out. I suspect the guy is her supplier ... as everyone else here does, so please tread cautiously on this one.
Drug dealing from a unit is again, different from drug usage. Many Dealers know the game and are absolutely great about paying rent on time and behaving so that there is no suspicion drawn to them. (If they are smart.) If they are dumb, careless, or arrogant, or if they feel they can't be touched, especially if they are safely ensconced in a nice community where the nice Manager is vulnerable to believing their "story," they will hunker down for the long haul.
One last note and then I will get out of this conversation today, I would also be very careful about going back into a unit where Maintenance has compelted the assigned work order request. I mean, Maintenance received the WO for a non-working A/C unit, attends to it, gets it working again, but notices what he/they consider drug items, they should CALL you to come over while still working. Once they complete the work order and leave, there is now no reason for you to enter the unit. If they still have work to do later and need to go back, then the work order is still active, and you could go back with them. All residents have the expectation that entry rules are respected. If the Resident is home, you can always go over and knock asking permission to enter. This is what I have done (and usually my Drug Task Force Officer is waiting at the bottom of the stairs while I knock and ask permission to enter ... such fun when they let me in then.