It doesn't look like she ever married
https://www.findagrave.com/memorial/217810420/isabella-sandilands
William Kidd married Rachel Sandilands
Name William Kidd
Gender Male
Marriage Date 8 Dec 1865
Marriage Place Dirleton, East Lothian, Scotland
Spouse Rachel Sandilands
1871 Scotland Census
: William Kedd Head M 29 Ag Lab N Berwick, Haddingtonshire
: Rachel Kedd Wife F 28 Gladsmuir, Haddingtonshire
: Helen Sandilands Mother-in-law F 70 N Berwick, Haddingtonshire