Sir McBiggun's sister
From Equestripedia, the Archives of Equestria!
This woman was a female Black Knight who may have been the sister of Sir McBiggun. Not much is known of her short-lived career as a knight.
In the "real world", she was portrayed by Applejack with a hastily put together knight costume made with a football helmet. While Big McIntosh and Trixie Lulamoon seemed to appreciate her presence in the Role-playing club, Snips and Snails (role playing as a elf and dwarf respectively) seemed to be bummed out that she ruined their game.