I've seen every episode including season 3. There was a Crystal Heart festival, but was anyone seen eating crystal berries?
yes, Applejack's part in the song "ballad of the crystal ponies" Applejack sings "made sweets from crystal berries" and popped one in her mouth though nopony was seen eating plain crystal berries in the fair
(looks through the songs in the My Little Pony guidebook) Oh, I see it now!