IMO, that mixture of drugs was a guarantee that she was not going to live. In the reports I've done with obvious suicidal ideation, I don't recall ever having a jumper, shooter, or slit wrister
waitasec
. All I can remember doing in 15 years are reports of intentional drug overdoses and in almost all of them it was with multiple drugs, with the people intent on killing themselves. The suicidal gestures tended to be one-drug overdoses, and they almost always called someone to tell them what they had done or planned it out so someone would come home in time. The ones who meant business took handfuls of what ever they could get a hold of. Some even stockpiled medication for the big event.
So, in my opinion only, I think M wanted to make sure she wasn't going to be saved. I think she slowly gathered the medications, borrowing them here and there from friends, dipping into the supple at home in a non-obvious way, until she was sure and ready to make her move. Getting dressed up, putting on makeup the night before makes sense, too (some people care how they're found), and I think she may have said goodbye to dad that night, as well. The jewelry could have been given away to friends.
If she was murdered, I think the combination of drugs is odd. It would be much easier to get heroin or cocaine or meth on the streets, plus it would have had the added effect of looking like an overdose, making her look bad in the process (remember that book, Go Ask Alice?).
As for the stalking, I think there was a peeper who got scared away, then people got jumpy and imaginations went a little wild and accusations were made. Then I think the people accused (the police supposedly went and talked to them) may have gotten mad and decided to retaliate by being nuisances.
If that is what spurred the suicide, then I think they are partially responsible, but if that wasn't the reason she did it, then I don't think anyone should be blamed by providing her with a sleeping pill to help her sleep, not knowing what she was planning.
That's just one possibility that I'm leaning towards.