This is a real outside chance possible (even for me!) but I do think it may be worth checking out.
Having failed to find your Edith Mary/ or just Mary in 1901 I had another firkle in the newspapers
I found this In Memoriam in the Shields Daily News 14 Aug 1901.
There was a marriage of a John Carse and an Edith 'Maughan' Johnson in Q1 1892 Tynemouth 10b 287. I know its a long shot but 'Maughan' is phonetically near enough to Mern/Morn to be possible and we know that name was used by your Edith Mary's brother Andrew Peter for two of his children.
Marriage Locator site.
http://www.marriage-locator.co.uk says it was at Christ Church.
There is a death registration for an Edith Carse (no middle names given) in Q3 1899 Tynemouth, age 29 which looks likely, though the age is a couple of years 'out' from the In Memoriam
also a birth for the little girl Edith Jane Carse
Q3 1899 Tynemouth, Edith Jane CARSE mmn JOHNSON
and a corresponding death registration for her Q1 1900 Tynemouth age 0
North Tyneside Local History Centre ( I think) have this marriage register on microfilm. If you are in the area then it would be worth a visit to see what the marriage record says about her age, her father's name and occupation and any witnesses all of which could help to confirm/deny if its your lady.
Boo