For a girl who gets a lot of positive attention after she fills in, Frankie sure has a cynical take on boobs:
Boobs are just inherently undignified. Those are what I've got that keeps me out of the Loyal Order. (31.44-45)
For Frankie, her breasts are the very reason that she's excluded. They signal her gender to all the world. Basically, she doesn't get to play with the big boys and be respected in the same way because she's a pretty girl with a curvy body.
So when she pulls off her first prank, she tries to provide some commentary on this. She makes sure that all the statues and paintings on campus are outfitted in bright bras, even though they're all of men, and wonders,
"Couldn't it be pointing out how there are like, no women in any of the paintings on campus?" said Frankie. "Could it be saying, 'Where are the women to fill out these bras?'" (33.38)
In a way, it's not breasts that are the problem. It's the fact that people think less of them or think of them as merely decorative. It's the fact that people don't take women seriously that's the problem, and the fact that there aren't enough of them in positions of power at the school (or in general).