Acacia

Acacia was the eldest known of her branch (ha) of the Pie family. She appeared to either be the older sister or possibly mother of Oak, Spruce, and [Birch]], but her exact relationship in the family unclear. She attended Partypalooza and seemed to have a high opinion of Cheese Sandwich.

Behind the scenes
Acacia first appeared in but wasn't named until the bonus interview in the end. She bares a striking resemblance to Mudbriar, hinting that at the point in time of Friendship is Magic: Season 10, Mudbriar and his family were now considered 'Pies', but this is unconfirmed.