After watching Nancy and Jane this evening, I have different thoughts about this case.
With the possible sighting of Haleigh in Mass., I think when Misty claimed "I'd never do anything to hurt that little girl," she could have been telling the truth.
Suppose she needed to get rid of Haleigh. Remembering Jr's account that the couch was bouncing, it could be Haleigh, who was supposed to be asleep in the bed, went into the livingroom and saw something like Misty fooling around with another guy. After the fight, we are hearing she and Ron was supposed to have that day/evening, having Haleigh witness something like this would be a disaster for Misty concerning her relationship with Ron.
So, because Misty knows Haleigh will tell her father what she saw, as well as a five-year-old could understand, the need arises to make Haleigh disappear. Yes, I really believe Misty would go so far as having her brother take Haleigh in order to cover up what she'd been up to.
So, the brother helps out and then along with his wife high tails it out of town with Haleigh in tow. And Misty stages the scene and goes into her act with Ron.
It is after all, jmo.