Terri Belle

Terri Belle was the eldest known daughter of King Diomedes and appeared to be a high ranking individual with Royal Guard-like gear. She was the elder sister of Blonn Di, Shining Light and Swift Foot.

History
Very little was known of Terri Belle, she didn't appear to be as antagonistic as her sisters, Blonn Di and Shining Light, but in general didn't appear to be very emotional. She stood by her fathers side with a spear in hoof while he told his youngest known daughter, Swift Foot, a plan to infiltrate Equestria in order to make himself the King of Equestria.

Behind the scenes
Terri Belle first and so far only appeared in and was likely created by Ian Flynn. Her name is presumably a pun of the word "terrible".