A red flag to me is why Billie would try to hide SA having left work on the 27th, when she first went on NG. Why do that? She had to have known she would be made to look as though she was hiding something.
IMO, the only logical explanation is that she didn't want people to think SA had anything to do with Hailey going missing.
The REASON she didn't is still up in the air, IMHO.
Is she is denial?
Does she feel guilty because she let SA move in?
Was she involved?
Or....something else?
Don't know yet. I'm still fence sitting. (We need a smiley for that).