Why put so much effort into buttressing meaningless linkage when the linkage already exists. JR/PR/BR occupied the same house the night of the murder. All three are linked by that fact alone. That BR's tdna is on a nightgown means nothing in itself, as there could be a hundred innocent explanations - all of which boil down to this - he touched her nightgown, at some point. Exceptionally unexceptional. That the nightgown was in the WC is important in and of itself, but it adds nothing to any theory of BR's involvement as we do not know when BR touched the nightgown.
We may equally assume that it had been out of the drawer for a couple days, laying on the floor of the bedroom, or folded on the footboard, and so on. The housekeeper was off duty and PR wasnt' much of a tidy freak as far as clothes and such.
He's already linked by having been in the house. Again, the tdna is virtually meaningless as he may have touched it innocently earlier in the day.
But JBs fingerprints are nowhere on the tea glass, or the bowl. You have failed to put JB at the scene. BR may, as others have suggested, took a few pieces up to her in her room.
No, it seems she was in her bedroom, then in the basement. Seems the same for the nightgown. No evidence she was ever at the breakfast bar.
Aside from the obvious problem of basing an assumption on an allegation, it would seem that her "aritfacts" are unsynchronized. Her PJ bottoms alleged to be in her room cannot be said to have been on her the night of the murder. She appears -by artifact- nowhere at the pineapple party. Sure, she ate pineapple, that's beyond question. But where? She ate at the table w/o touching anything? Her nightgown follows her to the WC, seemingly, but then her ljs also seem to have followed her down there. Obviously one or the other was unsynchronistically brought down at another time, unless you figure she was wearing a pink nightgown over ljs.