You... you do realise some of them were assisting Garrosh quite happily, right? Not all, but some.

Regardless, calling her a "bitch" (a notably derogatory term, I might add) after everything she's been through? The emotional trauma? Uh, yeah, I'd like to see you suffer through that and then be all happy and welcoming to those who, until recently, you believed to be the cause of the pain. Even though she knows now, it doesn't mean it'll be easy for her to come to terms with it all. That is the nature of trauma - you don't just flip a switch and wow, everything's fine. Even though the rational part of her knows that it was only a tiny percentage of the Horde that caused what happened to Theramore, trauma makes you irrational. She can't help but associate the Horde with that pain, even despite knowing otherwise. Plus it's not just Garrosh's actions - her eyes were metaphorically opened to all the destruction the Horde has caused over the years. Before, she defended them, tried to rationalise their actions, downplayed the consequences, because she wanted peace. And even despite her relatively neutral stance, she suffered at the hands of the Horde - as did the Kirin Tor, who were a similarly neutral party. That shock is enough to make anyone doubt whether their own past actions were justified and beliefs correct. She didn't just harbour anger towards Garrosh's Horde, but the Horde in general - of course, she knows now that the only true bad guy here was Garrosh and his close associates... but, fuck, she was traumatised by what she experienced - literally traumatised - and people keep reducing her completely justified distrustfulness and anger to nothing more than "oh she's just being a bitch."