My scientist mind tells me that these folks are desperate for someone to listen to them and are willing to twist themselves into pretzels to make that happen.
Here's what I believe:
This healthy 20-year-old girl did not die of natural causes.
The true cause of her death is unknown at this point.
None of the drug formulations in her body can be sourced to the home.
Stalking can and does occur surreptitiously.
The objective evidence we do know about (picture of stalker, keying of car, blade left on property) indicates M may have been a target.
Not enough investigation was done to rule this a suicide with any confidence.
I understand these are your beliefs, but with all due respect, we don't know she was healthy. Her own mother says she had circles under her eyes and was showing signs of stress, not eating, etc.
The cause of death was amitriptyline toxicity. It's the manner of death which is in question.
Can the drug formulations be sourced to her friends or outside sources available to her? It didn't need to come from the home to be suicide.
Yes, stalking absolutely can be surreptitious. So far, though, all we've really seen is peeping. The car she thought was following her may or may not have been a stalker. It could have been angry teenagers accused of stalking her trying to mess with her in retaliation for being questioned.
The evidence is inconclusive, as the picture of the "stalker" has yet to be identified; could have been a nosy neighbor. The keying may or may not have been related, and the blade on the ground was found AFTER they had moved out so there's no saying how long it was there. There has been only one footprint (as of yet), even with all that activity, and since mom was witnessed to more incidents than M, if there was a stalking or other predatory behavior, it could have been directed to her or even the whole family to instill fear.
With the evidence we do have available, it's more likely to be suicide than homicide, although we still have weeks of story to hear. The scenario of a poisoning in her own home by outsiders with such a large amount of medication, despite extensive security measures, is a lot harder to picture than one where she gathered the drugs and took them all herself.
I'm not ruling anything out, but from what I've seen, heard, and read since this thread has been up is that this is a very sad family trying to make sense of their daughter's sudden death, and perhaps not being able to deal with the facts.
I agree with whoever said that LE and the ME need to sit the family down and walk thru each piece of evidence (not dismiss them, but explain them) until the family can come to an understanding or until LE/ME says, "Hold up, you might have something there." As long as they don't explain there will be questions and accusations of incompetence. The family deserves to have all their concerns addressed, have access to all reports, and have the opportunity to ask questions until they have no more questions to ask.
They should take an advocate not related to the family (someone who can objectively observe and take notes) and be scheduled for an open-ended appointment. If it takes all day, then it takes all day. Any person of compassion should agree with that, and if they refuse to grant the family that, then there
is a problem.