SCOTT
JESSIE
39
YOUNG
F
1855
778 / 1 / 54
Selkirk Burgh
Jessie Scott
Vital • Scotland, Civil Registration, 1855-1875, 1881, 1891
Jessie Scott person details
Name Jessie Scott
Sex Female
Age 39
Birth Year (Estimated) 1816
Father's Name Walter Scott
Father's Sex Male
Mother's Name Janet Young Scott
Mother's Sex Female
Spouse's Name Walter Scott
Event Type Death
Event Date 6 Oct 1855
Event Place Selkirk, Selkirkshire, Scotland, United Kingdom
So this means that Mary Scott was born around 1854 hence why her birth is not in the Statutory records, and the church records are not complete. The only child of Walter and Jessie that I could find is Thomas.
Jessie Scott was registered Jessy... and her mother Jean Young was sometimes called Jane and Janet Young... and her father was... Walter Scott, same name as her husband. No wonder you found it confusing

SCOTT
JESSY
WALTER SCOTT/JEAN YOUNG FR135 (FR135)
F
15/10/1815
795
20 / 15
Lilliesleaf