After the Japanese games magazine Famitsu reported that Sunny would appear in Revengeance, series creator Hideo Kojima confirmed the news with a tweet.

Sunny is the daughter of the character Olga Gurlukovich, and was last seen in Metal Gear Solid 4: Guns of the Patriots. She appears older in this new shot, and the PlayStation Universe noted that she is wearing a pair of pants with the logo of Philanthropy (the organization founded buy Otacon and Solid Snake) in the picture shown in Famitsu.

[Thanks to Armando Alday for the news tip.]

Source: Hideo Kojima Twitter