'Katherine' was indeed Sarah Katherine/Catherine Holdcroft - birth reg'd Dec.1843 Lichfield - mmn Bowley - who was later shown as Kate.
She married in Scotland in 1883:
David McMillan Robb 32 Club Master 76 Haigh (or High) Street, Dundee, son of George Robb, Clothier and Jane, nee Wishart
Sarah Katherine Holdcroft 32 Schoolteacher Witnesham, Suffolk daughter of George Holdcroft, Hotel Proprietor and Sarah, nee Bowley (deceased).
Married 24/12/1883 Dundee
In 1891 Kate Robb is a widow but has a daughter - Georgie G. Robb who was born 13/5/1884 Dundee as plain Georgie. Clearly Kate was pregnant when she married. She is shown in 1891 living at Hawick, Roxburghshire, and a Certified Teacher, born England.
In 1901 she is in Edinburgh shown as Sub Matron of an Institution, born Staffordshire, England.
She died as Katherine Robb on 19/4/1923 Schoolhouse, Kingslassie, Fife - shown as widow of David M. Robb and informant was son in law (present) Norman Johnson. Correctly shows her father as George Holdcroft but mother shown as Sarah (correct), nee Appleby (wrong - as shown on her marriage certificate and her birth her mother was Sarah Bowley).
For a schoolteacher she was not very good at maths - she was born late 1843 but in 1881 states 36, married 2 years later as 32, in 1891 she's 40, 50 in 1901 and 77 when she dies 1923!!
Daughter married as Georgie Graham Robb to Norman Miller Johnson in 1912 St. Giles, Edinburgh. Norman was a school teacher too. Husband David McMillan Robb died 1891 Hawick (presumably just before the census).
Annette