Its not usual for me to voice an opinion, however lurking and taking on board others opinions, I wondered if we were looking in the wrong place? I have searched the threads, and maybe this has been covered, so forgive me if so....
I don't think the bath surround could have caused the head injury (in my non professional opinion!).
What if... PR and JB were in the bedroom, JB is tired, wants to fall into bed in her clothes, but PR is insistant she changes for bed... what if PR trys to remove JBs top and a scuffle ensues, JBs top is caught around her neck and PR is pulling and pulling, unaware that her actions are perventing JB from breathing. As JBs body becomes limp, and she loses consciousness, PR realises something is wrong... and lets go of the top, causing JB to fall forward and downwards... straight onto the edge of her bed. If you look at the photos of JBs room, each of the beds ends have scrolled posts protruding (sp?) slightly higher than her mattresses.. could she have fallen onto one of those? Like another poster (I'm sorry I forgot who) suggests, the injury is consistant with a rounded object.
Also the smell of peroxide could be confused with domestic amonia used for, amoungst other things, cleaning intense stains from carpets and upholstery.