I feel if AM took the action of suicide, she would have been found. On the other hand, as far as we know the searches in the area were minute and sloppy. I wish they'd have a full on search in the area around her car so it could finally be ruled out and we could move away from the suicide theory once and for all.
Quote respectfully trimmed.
I have no experience looking for bodies, and I don't have a good sense of how much undeveloped land there is around where her car was found. I do spend a lot of time outdoors and live in a rural area, though, and have a sense of how smell carries, and how animal corpses decay, and what they attract along the way. With spring, you have all the undergrowth greening out, but I have a hard time believing no one would notice the smell of a body left near a trail used regularly. And suicides can't bury themselves. If she was near a trail where people walk dogs, off leash dogs would be likely to be drawn over. But I could easily be off in terms of the temperature when she went missing, or the size of the area near the car/walking trail.
All of which means, yes, I agree with your sense that she likely would have been found, though I also acknowledge my lack of practical experience in these matters.
If her coworkers or friends didn't pick up on any changes in her--cancelling dates, not returning calls, flatter affect, decreased ability to participate in conversations, lack of joy in things that would have made her happy before, etc--she could have simply been high functioning while depressed. Or she could have not been depressed. Or they could have noticed those things because she was suffering from other life stresses.
It seems like there are a list of questions that only her friends and family could answer. Was she open about being clinically depressed/requiring treatment? Did she question whether she might be depressed? Did she begin to avoid people? Did her mood shift? If so, did she give any reasons for it? Was she anxious/worried/afraid about anything? If so, did she give reasons for that? Were they plausible reasons? Was she more angry or sad than usual? Was your gut sense that something was off, even if there was no proof?
Again, the answers to those questions could come back similar for someone who was depressed for biochemical reasons, or for someone in a bad relationship, or for someone uncovering an issue at work or about to lose their job due to cutbacks.
One last thought, following TrackerGd's statement about lost people being soothed by water: if she was sad or depressed, she could have been drawn to places that soothed her, or where she had been happy before. If there was a place in the neighboring woods that felt that way for her, I would feel better knowing someone had searched around it.
Ultimately though, I don't think I'm down with the suicide theory.