The info about Taylor's Close, Greenock is from his birth registration - I've just been looking at if - almost word for word what you quoted - formerly domestic servant, etc.
So Mary must have been at least in her late teens, I would think.
I've found four possible marriages for her in Paisley andLochwinnoch (near by Greenock) 1883, 1885 and 1888 (2). She could,of course have married in Lanarkshire or elsewhere

Unfortunately SP is being very slow tonight so I might have to leave any more checking until tomorrow.
There was a Henry Gilchrist on the 1881 with grandparents in Midlothian but I wasn't too sure about that as the age was a bit out - but census ages can be misleading. Maybe Darlene or Ethel might know of any possible relatives there.
Regards
Gadget