I dunno. She’s good, but I’d award Rarity as the best sister. Applejack would be an easy choice, but I like the dynamic between the two unicorns. That and how understanding Rarity was during the Gabby Gums thing and even tried to help them. {She gets points for not being a jerk in that episode} That and how much time and effort she puts into helping her little sister, such as in Sweetie’s dream episode and how far she’s willing to go, Sisterhooves Social.