My 4xgtgdmother is Janet CLARK daughter of James CLARK & Elspet ANDREW, who moved from Mains of Buckie, Rathven to Raemore, Deskford in 1771: their MI is in Rathven churchyard and is exceptionally informative although disintegrating fast. Although there is no baptism record for her, and no record of her death that I've found, there is highly convincing evidence that your Ann CLARK is sister of my Janet CLARK - the most obvious perhaps being her marriage in the Deskford OPR: "TAYLOR & CLARK: James Taylor in the Parish of Rathven & Ann Clark in Ramore having been matrimonially contracted, after regular procedure were married. Pledge returned."
I have estimated she was born in Jun 1759, almost certainly in Mains of Buckie. The witness Elspet CLARK you mention is Ann's younger sister, born 20 Jun 1776 at Raemore (and baptised at Rathven Episcopal church). And the baptism of James TAYLOR born 26 Feb 1795 in Knowhead was witnessed by James CLARK in Raemore who was Ann's brother who was well-known to the Kirk Session for having quite a 'complicated' life. James TAYLOR m Barbara FLETT, and I believe I'm right in saying that his brother William TAYLOR m her sister Margaret FLETT; another brother Alexander TAYLOR m Isabella HECTOR; and it seems likely that sister Helen TAYLOR m William GEDDES a grocer in Findochty (and not a relative of mine) although I've haven't got as far as checking this out.
I haven't identified William CLARK in Hilton but he could well be another sibling of Ann - William CLARK b Raemore, bpt 12 Aug 1774. Lastly, the witness to Alexander TAYLOR's 1798 baptism is yet another brother Alexander CLARK (who marr Isobel SHEPHERD and was a long-term tenant in Mid Skeith, Deskford.
Hope this is consistent with what you have already.