My great great grandmother was definitely Mary Robertson, not Collier. Her mother may have got married later, but I have no details.
William Leighton, her husband was a shoemaker, and my great grandmother was her daughter Agnes.
There are a couple of marriages recorded for William Leighton, but I am not sure that either are my immediate family. There were a lot of Leightons in Westmorland at that time.
Please tell me where you are seeing entries for Mothers Maiden Name, as this isn't recorded on the census.