It does seem more likely that she had passed out. If she was asleep, it seems that the girl could have roused her enough to unlock the cuffs.
You don't know that. She could very well have just fallen asleep. The girl, however had to have been up to something for the incident to happen. That is what I want to know. Teenage girls can be a handful. The girl could have been on the phone all those hours complaining to her boyfriend for all anyone knows. We don't know if she couldn't go in and wake the mother. The girl could have up and decided to call the cops herself to get mom in trouble. There's a whole lot of the story missing. For all we know they could have been the daughter's own pink fuzzy handcuffs.