Your Mary could be the sister of John McKechnie. They both show up on the 1881 Census in Winnipeg in the same household. Mary was 21 at the time of the census. John began an ironworks business in Winnipeg. They were the children of Stephen and Margaret who settled in Elsinore, Ontario, which is just west of Owen Sound, Ontario. After the 1881 census I have no info on Mary.
If you believe that this is the same Mary please contact me and we can share info.