Hanako doesn't deserve to be forgiven after pushing her that far. Just because she suffered alone doesn't mean she has the right to make someone else suffer as well.
Ugh, no, you just don't go and "forgive" the bitch who had tormented you for her own gain, even for the sake of guilt-tripping her to shit! Seriously, I've never liked this kind of logic in shounen mangas.
Yonagi didn't say she have forgiven her yet. She only asked why Honako is still suffering like the princess in the play, all by herself. The rage, the sadnesses and the loneliness. When Yonagi is acting she feel what Honako is feeling and just like her, she started to lose herself as well but was save by the other actor. She realise she have support which help her break free and by asking Honako this question will hopefully help her understand that she can break free too.