This does seem to be the logical theory based on what LE has said (of course with the caveat that they know NOTHING for sure). Following that theory, the only reason I can come up with is that the perpetrator believed there was a severe psychological or physical threat against Abby. But, then, it would follow that the perpetrator knew her well enough for either Abby to have confided in him/her or have formed their own perceptions based on interactions. IMO.
When I was 14, there were pretty strong threats to my mind and body because of the situations I put myself in. My parents, who were otherwise great, seemed to have checked out when I was a teen and couldn't parent well because they were trying to survive themselves. Luckily, i was never abused just neglected. But this led me, and only me, to get "love" from the wrong people and dally in drugs. My point in sharing this is that if someone around me at that time "cared" to extract me, to protect me from myself, I may have listened to what they had to say. I would have considered them safe because they cared.
But, that was me. Only Abby's family and friends know if Abby may have needed "help" with something. And, I can't see them letting anyone other than LE know if it's possibly a factor in her disappearance.
Does anyone else have any ideas along this line of thinking?