I would have thought the crimes would have to be non-contact looking at Sheila's hands, nightie and fingernails. Under those circumstances I just don't see it: some people want Sheila to be psychotic to the extent that she had control of herself and others, yet conscious enough to have planned the removal of the sights, the bedroom telephone and to avoid Police upon their arrival.
(a) Collins' assertion was right and she never was actually downstairs at 7.30am
(b) Sheila was downstairs but only 'playing possum' - which is how she managed to get upstairs when the opportunity arose. But
how was she assessed as being dead - if she didn't yet have any gunshot wound?
(c) Sheila was downstairs but her initial gunshot wound, whether a botched suicide attempt or the result of a Mike Tesko / Woodcock theory, was superficial (in the sense that it allowed her travel upstairs before collapsing etc).