Acacia

Acacia was the eldest known of her branch (ha) of the Pie family. She appeared to either be the older sister or possibly cousin 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.