I think she was manually strangled first by her shirt collar,per Dr Werner Spitz,and the head injury followed next...which IMO,was done with the flashlight,with INTENT to kill...I know a child's skull is softer than an adult's,but I just can't see that kind of head wound happening by accident...and the flashlight appears to fit the wound perfectly.Perhaps JB's hair and or her shirt padded her scalp,and that explains the lack of outward apparent injury until it was discovered upon autopsy.
The fact the scream was said to have ended abruptly was when the head injury occurred,IMO.And since JB didn't have defense wounds to her hands (that we know of,anyway),and that injury was off to the side of her head,I believe she was being held down low,near the floor,perhaps between her killer's legs,(perhaps she was jerked up from the floor by her shirt collar),when she was struck.I think the marks were from Patsy's rings,as there might be more pressure from them if JB were struggling and being jerked around on the floor.
Also the fact she was manually strangled,but yet still screamed,leads me to believe she broke free of that at least once before being struck.
The mark that was on the side of JR's face early on,leads me to think he tried to get in between the struggle between Patsy and JB,and got hit in the process,perhaps if Patsy was swinging the flashlight around.But..I don't rule him out as the perp,either.But Patsy's ring imprints and her guilty behavior lead me to think she did it.Ultimately though,I think it was JR's call that JB be denied medical help,due to past abuse.And then so the garotte was applied,and the staging began.The so-called infamous 'ransom note' came next.Next,I think phone calls were made,and perhaps a tentative plan to 'deny her remains' per the RN was made,with that plan falling through,for whatever reason.But I don't think the initial plan was to leave her in the WC.I think that was just a temp. hiding spot for her body at first.
So they were both involved,and I think that's obvious from their behavior.