Honest, Patient, Kindhearted
I think the thing that motivates Hero is how things will be once everybody knows the truth about what happened. She's devastated that no one believes her, especially Claudio since she probably thought he would always believe her no matter what anyone has said. In Act 4, Sc.1 she says, "They know that do accuse me. I know none. If I know more of any man alive than that which maiden modesty doth warrants, let all my sins lack mercy!-O my father, prove you that any man with me conversed at hours unmeet, or that I yesternight maintained the change if words with any creature, refuse me, hate me, torture me to death." In this scene, she's basically saying that she didn't do what everybody is accusing her of and if there's any way to prove that she did it, than they have her permission to hate her and even torture her to death. I think she says this to show everyone that she's saying the truth and she has no clue what they're talking about.
Hero is only 18 years old, but she's already a really mature lady with a lot of strength. She is Leonato's daughter, who is a man of upper class. Leonato is furious when he finds out about the fake rumor that Hero slept with another man. In his point of view, she's already ruined her reputation and he even says that she should just die. In Act 4 Sc. 1, Leonato says, "Do not live, Hero, do not open thine eyes" This really shows how disappointed and upset he is of his only child. He questions why his wife didn't have enough strength to have another kid because he claims to not love Hero anymore and he no longer sees her as a part of his family. Hero still insists that it wasn't her on the balcony, she always says the truth even after all the hatred comments that she's heard about herself. I don't think she really changes from the beginning to the end except that she maybe gained more strength and she became more frustrated since no one would believe her.
Impact on Plot and Theme
Hero impacted this play in a very strong way because it was mostly based on her love life. She is an honest lover because she always sticks with her own words and she never lies about anything. Her relationship with Claudio is both Mania and Agape. I think it's Mania at first because it turns into a big mess when she finds out about the rumor about herself. Her face of confusion says it all when they're about to get married and Claudio says no to their marriage. It's also Agape because after everybody finds out the truth, they go back together and it really seems like nothing can bring them apart. I think Claudio realizes how much he loves her when supposedly Hero was "dead". His face of happiness shows how much he really cares about her and how he was a fool about believing everybody else when he should have believed her first.