Artist’s description from the tumblr post:

-Sweetie Belle is eight years old, the adopted daughter of Luna and adopted cousin to Spike, the two of them act more like siblings than they do cousins. Sweetie Belle never had a childhood spent with either of her birth parents: she has a note from them, explaining why they had to give her up and reassuring her just how much they loved her, and though she is questioning and somewhat sad over it, she believes what they said whole-heartedly. She’s the one who gets picked on the most, if only because she’s smaller and less likely to confront her bullies, but her friends and big cuz has her back. Rarity may form a personal connection with Spike due to their similar history, but Rarity is just as fond of Sweetie: the girl treats the cat like some sort of princess kitty, and she very much appreciates it. She kinda reminds Rarity of Opal too.