I'm not sure that Hero really changes very much from the beginning to the end of the play. She remains very trusting of Claudio, despite the fact that he publicly shamed her and refused to marry her at their wedding.
Beatrice and Benedick both learn that they really can trust one another and that marriage won't be such a horrible thing after all. When the play begins, they both swear they will remain single, and especially that they will have nothing to do with the other. But through the manipulations of their friends, they learn that what they wanted all along was truly marriage to one another. In addition, Beatrice learns that Benedick is truly a trustworthy man because of his willingness to fight Claudio for Hero's honor.
Claudio, I think (I hope!), has come to realize that he really can trust Hero to be faithful to him. Twice he was led to believe that she was disloyal to him (both times by Don John - come on, Claudio, catch a clue!), and both times he was shown that she really was "a jewel"!
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