It's a long shot but what if the little girl woke up and saw her mommy making out with some stranger and freaked out and fled this mess?
That makes a little more sense than the idea that the mom was somehow involved in the child's disappearance, "involved" meaning that she directly participated in removing the child from the house, etc. For some reason, this just doesn't strike me to be the same type of situation that Susan Smith and Darlie Routier found themselves in. There were several people present at the house the night of the "abduction".
Of course, this could help build a fairly solid alibi, like "I was having sex in the garage with a total stranger while my kid was taken." Oh, and your husband? "He was there too, doing a friend of mine." So, in theory, this would deflect suspicion from the "parents". But, sadly, I think I'm being too optimistic when I try to believe that Danielle ran away to escape that madness. Most likely BVD will turn out to have played a role in the disappearance.