I've always hated the Tyrells. Not just her, her entire family. They have a massive unearned sense of superiority. Also, the show tries to depict Olenna as this no-nonsense tell it like it is grandma, but in practice she just comes off as deeply unpleasant. Watch her first scene with Tyrion. She's just kind of mean to him throughout it, and then caves and gives him exactly what he wants. She didn't achieve anything, she just condescended to him for a bit and ended up being totally ineffectual. That's her whole character throughout the series until she kills Joffrey and frames Tyrion, and then it's back to business with her.
One of my greatest joys in the show was watching her admit that Cersei stole her future. Knowing she felt a moment of despair that deep made my heart leap, I only wish we could have seen the look on her face when she heard what her greatest enemy did to her family. No witty retort, no smart comeback, no wry grin, just the knowledge that everything she cared about in life disappeared in a flash.