Ah yes, Minty. Y'know she technically did appear in Gen 4, but only as merch and an Applejack recolor. Let's fix that, shall we?

Minty is the biological sister of Pinkie Pie, born a few years after Pinkie's birth-parents had put her up for adoption due to their financial status.
Nowadays, Minty's parents are doing quite well in terms of money due to Minty's Special Sweets Shop. Though Pinkie and Minty have yet to meet, Minty knows that one day she'll find her sister. As for Minty herself, she's a ditzy but optimistic young mare, running the aforementioned sweets shop in Manehatten. She never lets negativity get to her, instead opting to look on the brighter side of things.