I am so far behind so this might not be the case but MOO
What if BD dentist was in Snyder and SA dropped her off, went and got rid of the body, picked her up, and the money she took out was in part for her antibiotics, pain pills, and some grocery's. I know when I have to make a few stops instead of pulling out my debit card each time, I'll take out enough to cover what I think I might spend plus extra for the next day.
This could be why there is deception because BD didn't know anything, but after HD became missing her worst fears started to wander through her mind. This is what could give a deception on the poly.
I think BD mind has gone to He** and back, between trying to remember exactly the chain of events, thinking that SA did something, Blaming herself for even having SA around, knowing all her life story is out there, Scared to death for her daughter, feeling isolated, cops not believing her, cops saying she is a runaway, BD feeling frantic and not knowing what end is up.
I still think BD is innocent, and SA totally manipulated the entire thing. I happen to think that when they first met online that BD probably said she was into horror flicks too but no way to the extent he was apparently. SA's mind has been thinking of murders for a long time. He clearly hatched his plan, and made his GF a suspect in the process. MOOOOOOOOOOO again!