Hi David,
Thank you for your interest.
Weddit is not a spelling I would have thought of.
I didn't think of that variation myself - I had resorted to searching with a surname "w*t" by that point!
My starting point was the 1790 marriage in Kinnoul, Perth of "Elisabeth Weetit to Duncan MacGrigor" where her father is stated to be "the deceased Robert Weetit Weaver in the Isle of Bute".
Scotlands People only had one Elizabeth baptism to a Robert "Whittet" giving a mother Margaret Pitrikin but he is a Chaise Driver which didn't look likely. A lot of searching through the transcripts on FindMyPast gave me the Robert Whittet and Helen Nicol marriage in 1751 and the following children, occupations and locations.
1751: Marriage Robert Whittet & Helen Nicol - no occupation listed, both of this parish [Perth CofS]
1753: Jean Wittate
Robert & Helen Nukel - no occupation listed [Perth Associate Congregation]
1756: Hellen Wittate
Robert & Hellen Nuckel - (not purchased) [Perth Associate Congregation]
1757: Elizabeth Weddit
Robert & Helen Nicol - father weaver [Perth CofS] Elisabeth Weetit on marriage and assorted other variants on her children's births
1759: John Weddit
Robert & Helen Nicol - father weaver [Perth CofS]
1761: 6 April 1761 listed in an advert in the Aberdeen Press and Journal for Gordon's Milns Bleachfield as "Robert Wittet" at their manufactory in Aberdeen
1761: Catharine Whytet
Robt. & Helen Nicol - father Clerk to the Gordon's Milns Company [Aberdeen CofS]
1764: William Whittet
Robert & Helen Nichol - father weaver [Perth CofS]
1766: Robert Wittet
Robert & Helen Niccol - father Clerk to Mr John Blain Commissary of the Isles [Rothesay CofS]
1769: Thomas Wittet
Robert & Helen Niccol - father Clerk to Mr Blain Commissary of the Isles [Rothesay CofS]
FindMyPast does have a baptism for "my" Elisabeth but it is currently unindexed on Scotlands People and I have queried that with them. I actually found it by fluke on the same page as her brother John so it is definitely in there.
I am still not 100% convinced that there aren't two Robert and Helen couples here but all the dates make sense and I need the location on the last two births to make this fit the reference on the 1790 marriage so....

Maybe it is Elizabeth thinking of her Dad as a basically a weaver even though he had been promoted beyond that by the time he actually was on Bute.
I haven't manage to find any newspaper records or deaths/burials so I think this is as far as I can go for now.