I tend to agree with the case for the defence. Frost is a fantastic, complex, well-drawn character. How she chooses to dress and behave, and the contradiction between the tools she has learned to use and her sincere desire to teach is a vital part of that. That's the point of her, after all.
Which is not to say that what Frost says here isn't bullshit. Again, that's fine: it's exactly the sort of nonsense a character like that would say.
"There's no such thing as sexism, unless you give them power."
Look, it works for you, Miss Frost, that's fine. But you are a upper-class white woman with mind control powers. Check. Your. Privilege. If you can use sexuality as a weapon, to get ahead in a sexist world, fine. But it has its limits, as Rocket finds out in Sucker Punch (another thing that people who weren't paying attention wrongly think is sexist). I think that's a good examination of the sort of attitude spouted here by Frost. Valtyr writes of it very well:
Babydoll is dancing to distract men, and the other women are stealing items from men undercover of it, and this is terribly fucking dangerous. Sexuality is the only weapon that has been left to them, and it's a dangerous weapon to use because the second the men realise it's being used, it's over. When the music fails and the dance stops, the man notices what's happening; it's over. The music starts again, but it's too late. A woman dies. Again, later, a man is surrounded by all these beautiful women in scanty clothes; their sexuality can't save them, it's a weapon they're allowed. Women die. Babydoll can dance; Blue's got a gun.
The unnamed new hire realises this too. She knows the only way for someone like her to survive the Hellfire Club is to quit. So she will. While Emma continues living in the spaces that men allow her, even though she could do so much more.