Though I wonder - since it seems they might have known each other for a fair while - if she wasn't always like she is now?

That's my suspicion, because it would explain why Grace and Liv still feel loyal to her. But then what made her change? I think maybe Liv was complicit in earlier stuff like this because she said something like "It's not Year 11 anymore," implying that they used to do this stuff but she's grown out of it, but I can't imagine Grace ever being like that. Hmmm.