This definitely makes sense. It's just speculation that she hid or slept because no one knows.
My only question with your theory, which isn't specific to your theory, would be if she left her room and went downstairs to B, would she not have noticed blood? The PCA doesn't state anything about whether the person she saw had blood on him BUT you've just stabbed 4 people to death, there's blood on you. Unless he was wearing some kind of overalls/shoe covers which he took off and left at the scene (Xana's room), but that would be very risky for him, then there's no way there wasn't blood on him/his shoes that possibly left a trail on the floor. I totally think it's plausible D messaged B and went to her, I would just question how she didn't see blood in this instance. In some of the photos from the inside of the house, you can even see blood on the cabinets in the kitchen, but perhaps she just didn't look around and had tunnel vision to B's room
No one has seen the phone records. The info mentioned here is in the PCA.
"The combination of DM's statements to law enforcement, reviews of forensic downloads of records from BF and DM's phone, and video of a suspect video described below leads investigators to believe the homicides occurred between 4am and 4.25am"