Think it would be worth contacting owners of several online Cluney and/or Dawson trees to exchange information if you haven't done so already, especially the one that says Sarah, daughter of Thomas and Bridget, died in 1923 (giving NS vital records as the source). I did start looking for Sarah ? died 1923 N.S. but still haven't checked surnames beginning with m, n, r, s and t.
I did check online gravestone records on N.S. Genweb site for Gutsborough and found nothing although as Valerie says many markers may not exist.
Wonder if there would have been a write-up in any newspapers (either local or Halifax papers) about Christina (McDonald) Dawson's suspicious sounding death and possibly George Daawson's death.