Arguably Macduff of Macbeth by the time of Act 5, Scene 8 when Macduff fulfills the prophecy of the weird sisters(he can harm Macbeth) by telling Macbeth of how he was born, even to the point where Macbeth cannot believe it to be true:
Macduff: Despair thy charm,
And let the angel whom thou still hast served
Tell thee, Macduff was from his mother's womb
Macbeth: Accursed be that tongue that tells me so,
For it hath cow'd my better part of man!
Natalie by the end of Next To Normal. She goes from being an angsty teenager who hates her family and the life they have provided, to a happier young woman who acknowledges how much the Goodman household has been through, and wants life to "give me pain if that's what's real".
Veronica Sawyer from Heathers goes from a bully victim with a psychotic boyfriend to the new head of the school who shot said psychotic boyfriend before he blew himself up.