Important clue in the 1859 marriage is father Hugh Lamont is a cooper.
the Hugh Lamont in Glasgow, 1861, is a brick maker.
Civil Parish: Glasgow Calton
County: Lanarkshire
Address: 10 Fordnenke St
Hugh, 38, Mary 38, Francis 16, Jane 13, all born in Ireland, and a Christina Lyon, 18, born in Glasgow. I can't see the images at ancestry.
-----------
Question for the OP: Have you found them in Glasgow earlier than this?
Devil's advocate: What makes you say the Catherine who married James Dunbar is your Catherine? Did they later move to Glasgow near Hugh and Mary? Or are there later records that link her to them? -- I haven't looked yet.
On the other hand, the Catherine Lamont who married James D. was 16, had no occupation, and evidently was not living with her parents, since there were no Lamonts in that townland. Maybe she stayed behind, her parents knowing she would marry soon. If she was someone else's daughter, why wouldn't she be with her family?
Thinking out loud again.