Yes that's right.
She married Thomas Lochhead on 8 December 1899 in Blackfriars although Thomas was already married to someone else at the time. Thomas and Mary also had 2 children, George (1900-1900) and Thomas (1901-1981)
She died on 18th February 1909 in Cambuslang. Her informant was her son William O'Hara but he had changed his name to William Lochhead. Mary was also listed as a widow although her husband hadn't died until 1925.
There has been a lot of name changes between her children as different combinations of O'Hara, Lochhead, Mc/MacDonald.
I have Mary McDonald in 1881 and 1901 but can't find her in 1891. She could have any surname between McDonald, O'Hara, Roger and maybe something else I haven't found yet.
I know in 1889 she was living at 118 George Street and by 1893 she was living at 120 Saltmarket.