J.J. you are correct, I am sure that it is the correct Lillie Roscoe.
She appears on an Ontario census in 1901 working as a Domestic for a family named "Park" in the Hastings county which is very near Belleville where the Marchmont house was in the day.
It is thought that she passed away at a young age sometime before 1915.
Family folk lore has it that this message was passed along to another older brother in France just before the death of Albert Roscoe.
Would be nice to establish the location of her grave site etc.
It seems Albert came to Canada in 1893 I think in May on the S.S. Vancouver.
He also was processed throught the Marchmont House in Belleville and worked on a farm near Sterling Ontario.