Mary Highet, is in fact Mary Scoular, born 18/Feb/1817. Stewarton, Ayr, to parents Joseph Scoular, and Isobel Broadie, she is the twin sister of Janet Scoular, who is living with her mother Isobel, in the census provided in earlier posts.
Mary Scoular, married John Highet, 15/Dec/1838. Stewarton, Ayr.
This makes her John Scoulars, Sister.