For me, the question about the Bloomies is one that will probably always remain a mystery.
We only know JB was wearing them when she was found
and when she was lying on her belly as she urinated (when she died by ligature strangulation).
We don't know where those size 12 Bloomies came from within the house.
We don't actually know if JB went to bed that night or if she might have even dressed herself after she got home from the the White's.
We don't know if JB might have worn the Bloomies to the dinner party.
We don't know where the remaining 6 pair of Bloomies were.
Therefore, when it comes to the word "redressing" - I always pause for a minute. Isn't it possible that her killer pulled her britches down and then pulled them back up again after wiping down the mess they made?
In my mind, this seems more plausible than someone taking the time to change her clothes. jmo
(To the bolded) Yes. That was the point I've been trying to make. Sometimes, the simplest answer is the correct one. This is what I believe happened, because as you say, it's the most plausible. She was wearing those before the attack ever took place.