Her name is Swift Foot, from the IDW Comic: Feast of Friendship. In her comic she is sent as a spy by the King of Thrace Diomedes, who is also her father to destroy the friendship in Equestria. An important fact is that she has always been belittled and belittled by her three sisters.
For my canon of Equestria Girls it is somewhat partial; She convinces the Rainbooms to make a presentation on their Island, but it turns out to be a trap and the Spirit of Diomedes, the fallen King of Thrace tries to steal the magic from the geodes, something that would be relatively easy since Swift makes the 7 best. friends argue with each other; or that’s what she expected.
Left: Thracian outfit. Right: street/infiltration outfit
(Please help me with the tags)
Excuse me?