I know most people here seem to be leaning toward HT, and I'm definitely not ruling it out. However, I can't shake the idea that she could have been a CI. It would explain her mysteriously dropped narcotics transportation charges that someone here tried to inquire about by phone and couldn't obtain any more information. I was arrested in Los Angeles and detained a few years ago, but they let me go without any charges, and I don't have the arrest on my record, or on one of those websites. I assume the situation would be the same for M had her charges been dropped... but they're still visible, which is strange, IMO, and leads me to believe that something happened behind the scenes. It also might explain the secret she had to keep from her sister - CI's are instructed not to tell even their closest family members. In thread #1, Mistivon (I think) wrote that Sara said M's activity recently resembled that of when she was using - coming straight home from work, and not doing much else, if I'm remembering correctly. Had she been secretly working with police as an informant, that might explain the change in routine. Sara would have to think really hard about M's schedule and behavior in the weeks/months leading up to her disappearance, which I'm sure she already has over and over again.
Her phone going off incessantly in goodwill could very well be the key to her disappearance, or at least one of them. I really believe she went to meet whoever was calling her, but there's no evidence to support that since we have no phone records. It makes the most sense to me though. I keep thinking about the possibility that someone she used to know saw her and that's who called her.
The dog's scent trail is another thing - if the dog traced her walking into multiple rooms of the church, wouldn't the church witnesses have mentioned that behavior as well? They only said she looked sick/scared. It could have been a red herring and then, who knows what other parts of the trail are, as much as I absolutely hate to say that. I'm still keeping that trail in my mind though bc it led to what we believe are her items, I just hope they have gotten around to processing them so we can have some proof.
I really don't know what to believe. On one hand you'd think the police would let the family know sooner if she was a CI, but at the same time, I'm not sure of the process of keeping actual records of informants and their activity. I doubt some random desk jockey one of us gets on the phone from the West Valley PD has any access to those type of records. I don't think any LAPD officer would know if she was an informant unless they were involved in her specific case, or they did some digging/asking around. Which could have happened by now, and they could have informed the family, which would explain the privacy and attempt to retract any info that has leaked so far. Also, people involved with petty amounts of drugs might be more likely to give her up for $1000 than an organized HT ring, who would likely scoff at $1000.
Again this is all just my opinion, food for thought for all of you other sleuthers out there.
At the end of writing all of this I STILL don't know what I believe, because I can't fully back any of these theories with such little to go on. It all seems possible to me.