Serena in S15, E7 (spoilers)
This episode deals with gay marriage it seems that Serena is all for it, even refusing to argue before the NY Supreme Court that such a marriage is unconstitutional.
Nothing is said about her being gay, but, watching it in retrospect, I'd say she is and that McCoy and Branch were aware of it based on a few looks that they exchanged once or twice during the episode.
Have any of the writers ever spoken on the subject of her final line?