Smile Time - S5-E14
Character mistake: While Gunn and Lorne are interrogating Framkin he sings a couple bars of a song "Courage and Pluck". However, though he has the ability to read people when they sing, and in fact in the very next episode knows that Fred is about to fall from just the words "you make me happy", Lorne doesn't read him.
Answer: Nope, it's not Darla - that's Rachel from the episode "In The Dark", the third episode of the show (the one with Spike's magnificent opening monologue).
Tailkinker ★