Many children are accustomed to wearing underwear to bed, even under pajamas. My own grandkids do this, putting fresh pairs on after their baths and another fresh pair on in the morning.
Patsy was asked about this in one of her interviews (where they are discussing the too-big panties. She said that it would be unusual for her NOT to be wearing panties and she would have noticed that. So to me, that is one reason why she had to be redressed in panties after her own had to be removed. The Rs tried to stay within the limits of keeping her dressed the way she had been when they last claimed to have seen her- when they put her to bed.
BUT if this had truly been an intruder crime, she probably wouldn't have been redressed at ALL. For one, the intruder would want to get out of the house FAST, especially since she had screamed. Then too, an intruder would have not cared HOW she was found- nor would they even have hidden the body. Why hide her? Leave her under the Christmas Tree like a broken doll if hurting the parents was your aim.
I feel the sexual assault was what was really being hidden. Pedophiles that kill their victim usually do not care about hiding that fact, in many cases actually like to showcase their perversion.
The garrote, while touted by Lou Smit as a "sophisticated sexual device", was anything but, and did not function as a true garrote nor a noose. It was simply a cord with a stick (the brush handle) attached to the end. It strangled her, to be sure, but to call it a sexual asphyxiation device is quite a stretch.
If the stagers wanted to display the sexual assault, they'd have left her naked or left any bloodied panties there.
Because I believe the parents were the stagers, I think they simply could not bring themselves to leave her naked or bloodied. They dressed her as if she were readied for bed, just as she had been. They emphasized the "kidnapping" aspect by writing the note, but needed to add the garrote because there was no visible injury from the head bash, which I believe came first as a reaction to her scream. Immediately collapsing, she may even have appeared dead, or they assumed she would die imminently. How to explain that? Calling 911 was not a option- they knew there had been a sexual assault. Calling 911 and saying she died how? Coroners and emergency room personnel can tell if a child had really fallen down the stairs, off a roof, or been beaten. JB's body had no bruises consistent with that type of trauma. Her body bore few bruises- one on her shoulder (possible from someone kneeling as they tied the garrote knot- it was at the back of her neck) and there were a few small bruises in her vagina and a small bruise on her labia. Described as areas of purple discoloration, they are different from the "abrasions" that Smit said were from a stun gun.
It is true that someone looking at her wearing the panties, even still- even lying down- would notice their huge size. After all, the coroner and LE present at the autopsy noticed that very thing.
But looking at the BODY in situ would reveal no such thing. The panties could not be seen through the longjohns and their fit was not apparent.