I just thought of this...
You said that the
NANNY in 1916
Virginia used to call your grandmother "Ersell".
The term "'ersel" was often used by African American maids, slaves and staff to refer to a lady of the house, who was young. Kind of like "ma'am" for girls. It is short for "herself". If the nanny fit into this category, she may have started calling your grandmother this as a sign of both endearment and respect to her charge's position.
Just a thought.
______________________________________________
Mama to Clarisse and Nadine. Mahal na mahal from our little family to yours!