I hate to say this but the content of this case is disturbing, no way around that, so I'm just going to say it.
I wonder if Shaniya had been trafficked before that night.

I suspect that in the past, at least once, her mother gave her to him for this purpose. I think he felt an accord had been reached and she was "on the table" in future.
I suspect that night, McNeil began his games with Shaniya in the mobile home, was concerned about her crying out and making noise bringing unwanted attention. I think he was pizzed none of his F buddies was awake or available so he started with Shaniya, realized someone might awaken and interrupt and so, crept back out of the mobile home with her. I think that is why there was feces on the railing, he wiped his hands along it as he carried her out of there.
I also believe that is why she was wrapped in a blanket in the photo of them entering hotel.
Once in the room he could finish what he started without so much worry about the noise, cries, or being interrupted.
I hate this man so much. So much.