There are numerous inaccuracies in the details the poster has on this thread. Some perhaps due to mis-reading records and others perhaps due to family members trying to cover up illegitimacy and other scandals.
Starting with the incorrect 'facts' OP has given us- [my corrections in red]
(original post) Marrage was recorded in the Derry Journal May 27 1897. Cannot find marriage notice in Derry Journal 27 May 1897
In the 1901 census Townland of Lisclamerty, District of Kincraigy, County Donegal, Parish Raymoghey. John Stewart, her husband was not at home the time the census was taken. In the form John Stewart's name is crossed out as Head of the house and Ellen's name is added. Census doesn’t indicate that John Stewart was her husband. John Stewart was the person from whom Ellen Stewart was letting the property
In the 1911 census I can find one Ellen who matches the description of Ellen Stewart, she is married 11 years and is recorded as on her own but married 11 years. Original lists Ellen’s status as “married” with quotes around the word married
My grandmother was born at Tullymortans Tyrone, I have a copy of her birth certificate. Mary Kathleen Stewart was born on June 5, 1902, in Castlederg, Tyrone, Northern Ireland, the child of John Gerrard and Eliza Jane. Very strange because, as gaffy found earlier (reply #6), this record is completely different. (reply #3 gives mother was Isabella Duncan)
(reply #3) John's first marriage in Donegal. Although it was recorded in the Derry journal and Margaret was from the Parish of Ballindrait, Donegal. The Derry Journal readership covered an extremely large area. However, I cannot, as yet, find any trace of the marriage being announced in the 27 May 1897 issue (or any other in that period)
Mary Kathleen, father John Stewart, living at Tullydoortansm mother Isabella Stewart formerly Duncan, fathers occupation farmer, Margaret Duncan registered the birth… details on birth certificate The birth that gaffy found (more on this later) does not list a middle name and gives parents as John Lecky & Isabella Duncan
Her sister, Maggie Jane Stewart, was born on Jun 12, 1906… to Elizabeth Duncan and John Gerrard Stewart. This is the only other birth certificate I have found parents John George Stewart (farmer) and Elizabeth Stewart formerly Duncan, informant- mother Lizzie Stewart
Ellen Stewart died on December 4, 1917… Ellen Rebecca Stewart, father John G. Stewart
[1911] Daughter Mary was 8 years old at the time of the census, her father was a widower Mary’s age transcribed and clearly written as 7 not 8 and her father was widower not widow
Now, I've been checking records trying to figure this all out- see next post