I have a bit of a silly theory which I haven't seen mentioned in the thread yet, so I'm going to put this out there... please be nice; I'm new lol.
I think most of us are baffled why Asha went outside in terrible weather, without a coat. It's become more of a mystery than what happened to her at this point, because nothing fully makes sense.
I wonder whether the fact it was her parents' wedding anniversary accounted for her late night jaunt. Maybe she wanted to get them something from the convenience store (I'm not sure how close it was, but I think I read it was on the highway) before they woke. Maybe something for breakfast, and it couldn't wait until morning because she had to go to school. Perhaps the lights going down affected whatever plan she initially had, or her parents had, and she thought she could save the day?
I don't think she sleepwalked - we'd have probably heard if she had history of it - and without a clock in her room, mobile phone or the Internet, she wouldn't easily be able to arrange secret rendezvous with friends. It doesn't sound as though she was trying to run away as such; her home life doesn't sound bad, and surely she'd have at least taken her coat if she was planning to be away a long time, and say goodbye to her brother or leave him a note as they were close.
I think she was intending to return, perhaps grabbed her book bag as it had her key in it (perhaps it still had pyjamas leftover from the sleepover which she was yet to unpack) and headed out thinking it was a quicker walk than it was.
Does this sound stupid? Does anyone know how far the convenience store is from her house? Was it a 24-7 kind of place?
In any event, I'm not sure we'll ever know for sure why she left, but with luck the Dedmon sisters will cave soon, and hopefully give Asha's family some closure about her last moments