I do not know who Helen's parents are and our chat is part of me finding part of the proofs to the answer. Helen seems to link to all the Clark in a way.
OK. That's fine. My concern was that many others had come up with at least two views as to her parentage, one of which can be dismissed out of hand and another is unlikely, and I couldn't tell whether you were coming from their direction or not. But I'm surprised that Rev Weir didn't know her parents but knew her sister. Which is why I was pressing. And still am!
But, before dealing with Helen Weir ms Clark, some findings on the Simpson side.
a granddaughter of the said Elizabeth Clark a Elizabeth Simpson married a James Mitchell from Park Home Dufftown 4th March 1820 this is tracible or proven, and therefore possibly makes her mother Jean Turner who is recorded having resided in Crossburn before being buried 30 JAN 1821. Dying of course first. Why parentage is an uncertainty because there is a Margaret Turner marrying a John Simpson 1787 in Keith, but no Jean recorded to my knowledge
As it happens, I have James MITCHELL & Elizabeth SIMPSON in my tree database. And just to complicate things further, I now see he is a gdson of John ORD & Helen BURGES who are my 6xgtgdparents. I have their son Robert MITCHEL who died 27 Apr 1819 at Parkmore, Mortlach and his wife Mary Ord died 28 Dec 1830 at Parkmore (MI in Mortlach c/y). And the adjacent MI for the family of their son James MITCHELL, up pops the name of Elizabeth SIMPSON (LIBINDX's headstone refs M(O)48 and M(O)49 with Elizabeth erroneously indexed as M(O)89). I hadn't made the connection. Have now!
Now, that's a by-the-by in our discussion. But I can now trace Elizabeth SIMPSON. She died 16 May 1880. By coincidence I already had the page of her death registration which confirms her parentage as John SIMPSON & Jane TURNER (image attached). So John SIMPSON ought to be the son of Elizabeth CLARK? LIBINDX NM167159 has his MI: died 18 May 1846 age 86. So born abt 1760 (in Banffshire per 1841 census). His burial record shows Mr John SIMPSON 25 May 1846 Keith. And LIBINDX headstone Ke(O)434 shows he died age 86.
So, John SIM(P)SON was born abt1760. But no records show a Clark mother. So I need help here - where's the connection to (a) Rathven (b) Clark? I'm afraid I'm going to take some convincing that this Keith Simpson line is connected to our Rathven Clark line. But serendipitously this exercise has connected a spare branch that was lying around into my main trunk. So, as they say, that's all good.
That's the second of my three 'threads' I mentioned. Next I'll cover the Rathven Clarks you mention. As you know there are zillions of Clarks kicking about and whilst I and others had untangled them to a degree of certainty, there were and are all sorts of loose ends, one or two of which I'm trying to tie up as a result of your posting. Not just all those Burnsides (I remembered another one - Burnside of Tynet) but a surplus of Jameses and Johns. And when two cousin Clarks marry and one of them has both parents named Clark, you know you're in for a brain-squishing ride.