Sarra and I communicated a lot offline and discovered the person that she was researching for had a connection to the Bonnitcha's through the Bell line.
I have recently been looking into it again, and I think the people that my family has shared DNA matches with, in Tasmania and Canada, must have the nearest common ancestors of:
John Watson and Margaret Fraser married in July 1795 in the parish of Avoch in Ross-shire, Scotland.
John per 1851 Census born abt 1767 Avoch
Margaret of Kirkhill parish, Inverness-shire at the time of the marriage. No death found and not on Census.
I wish I knew how it connected through to us, but I think the above couple are likely to be the parents of Ann Watson who married Donald Fraser.