You're looking for chapter eleven, Hermione's Helping Hand.
That's it. That is Hannah's entire appearance in HBP, and it's only a report of the previous days events. We don't actually see her again until the end of DH. She isn't reported as being in the Room of Requirement, but she's guarding a tunnel with Lee and (Fred? - it might be George!).Originally Posted by Half-Blood Prince Chapter 11
As for her personality, she seems to be bervous during her exams, and rather quiet. As she later becomes a pub landlady, I don't think that she'd nurse a grudge, she'd certainly forgive minor misdemeanours. But I can't see her forgiving her Mum's killer.