It's going to be hard for you to be definite about anything I think. Marjory seems to have chopped and changed names, it may simply be that she didn't remember. So what do we have:
~ A birth entry in 1886 in Stevenston for a Marjory McGuire, parents James, a dock labourer b. Ireland, and Margaret Docherty b. Glasgow. We also have the family in 1891 with some reference to Saltcoats which ties up with you have heard.
~ Likely death in 1894 of mother Margaret Docherty (husband James, quarryman).
~ A possible entry for a Marjory McGuire in Blantyre age 14 working away from home as a domestic servant.
~ The 1908 MC for a Marjory Docherty to a Toby Wilders, both show-people in Campbeltown. Marjory downs as age 22 (b. 1886 which matches what we have) however she has put parents down as Patrick Docherty, packman and Margaret MS McGuire, both deceased.
~ The 1915 MC for a Marjory Docherty to a James Burns shows her as a spinster and age 28 ( birth year c. 1888), parents John Docherty, quarryman and Marjory McGuire (MS), both deceased.
~ I can't see a death for her under Docherty/Burns. Have you managed to find a death cert for her although going by her previous records, you will probably find differing info on it as well.
Regards.
Monica