My Mother was an orphan who stayed in this home. My understanding is that they only allowed children to stay there until they were 14. After that, they had to go somewhere else and couldn't stay at the home. My Mother had 2 older brothers - one was 14 when their parents died and he never lived in the home. The other brother was 12 and he was allowed to live there until he was 14.
My guess is that your great grandmother was too old to stay at the home.