Lessons
From Frex, Elphaba learned to be cold, sarcastic and impenetrable.
From Nessarose, she learned to believe in something so strongly it became the only thing that mattered.
From Glinda she learned hair-flipping, and elementary fashion, and how to attract boys, and friendship.
From Fiyero she learned that even a green girl can be loved.
From the Wizard, she learned to be wicked.
From Elphaba, Glinda learned to believe in something that matters, that she wasn't entirely brainless, and that anyone, even a cold, sarcastic, impenetrable green girl, can love.
In short, from the Wicked Witch, Glinda learned to be good.