Angryverse/Ruby

Ruby (also known as the Female Red Bird or Girl Bird) is a bird that resembles her male counterpart Red, but has eyelashes, different pupils, thinner eyebrows, lighter spots, and wears a yellow bow on the top of her head (though it is blue in the free version).

Basically, This is the Minnie Mouse/Daisy Duck syndrome.

Hogs and Kisses
Ruby wasn't used as a playable character, but instead as a background character used to promote this section of the game, but despite that, she does make an appearance in the end cutscene when completing Hogs and Kisses.

Angry Birds Friends
Ruby makes her reappearance in Angry Birds Friends, though this time, she was only used as an avatar.

Angry Birds Evolution
Ruby makes a cameo on Peck Girl's baseball bat as a sticker.

Plush Toy
A plush toy of Ruby was released in 2011.