If those ponytails (especially the lower one, at the nape of her neck) were done as staging, the only reason I can see for that, as you mentioned, was to throw attention to the garrotte. BUT 2 things bother me about this. First, there was no apparent bleeding (from a skull wound,at least), break in the skin or swelling of the skull since the bash occurred so close to death. So there wasn't really anything to hide. From what I've read, even the coroner was surprised to find what he found when he did the autopsy of the skull and brain. If she had lived much longer after that bash, her head would have been VERY noticibly swollen.
The second thing involves the hairties. The one at the top was held by 2 hairties, one blue and one red/black/white (I think I recall that). The red/black/white WOULD have matched her outfit, whether she was wearing the white shirt or the red turtleneck. PR was also wearing red/black/white (her patterened woven jacket). I have seen JBR with just one ponytail as a topknot with the rest of her hair down long. The blue hairtie could have been used to make the ponytail, with the colored one added over it to match the outfit. Girls use this method all the time, with scrunchies and such. Then, for bed, the second lower ponytail could have been made by PR as she was getting her ready for bed. I think most of us agree, what with BR's statements and such, that JBR wasn't really asleep when they got home, and did walk into the house that night. I do find it plausible that on a late night with an early start the next day, that even though she was awake, PR could have simply pulled the black velvet pants off and pulled on the long johns as she said she did. So she could have had time to fix her hair for bed, just kind of pulling the long ends back into another ponytail. The fact that there were hairties scattered in JBR's bathroom leads me to believe that this is exactly what may have happened- with a sleepy and irritable JBR and a stressed out and possibly "tipsy" PR arguing about whatever (maybe the pineapple snack) and well...one thing led to another.