Does anyone know why Kate never called Mary as "Mother" (even if she knew her since she was 3yo) but the twins Oliver&Amanda called Eloise "Mother" right after her wedding to their father Sir Phillip ? (and they were older, 8yo) ?

I know Julia wrote that Sir Phillip chose to remarry — and chose Eloise, that is — because he felt like the twins needed a mother to "school" them a bit, but almost the same was said about Kate's father; that after losing Kate's mother so horribly when their daughter was 3 years old, he felt like she needed a mother and that's why he remarried so soon after Kate's mother's death....

And I know Kate loves Mary fiercely (she even named her last daughter after her!! See the 2nd epilogue from When He Was Wicked) but I really can't understand why Kate never called Mary "Mother"....