Speaking for myself, I think JB said something P REALLY didn't like and Patsy grabbed her by the collar and waistband and went to throw her onto the bed, only she mistimed it and JB hit her head at high speed.
They didn't want him as a witness.
If that be the case, why wipe down the flashlight so thoroughly? Sorry, I just don't see Patsy being able to pick up and throw a 60 LB child with enough velocity to do that much damage.