Zina's a girl in Sasha's class, whom Sasha describes as a bit of a Queen Bee. She "always speaks for everybody" (18.6), which means she's got some guts. When Nina Petrovna demands that all of the kids write down who they suspect of breaking the Stalin statue, Zina is the only one who has the courage to tell the teacher she's not writing because she's not sure who did it.
She's not totally immune to Nina Petrovna's steely Communist stare, though. We don't blame Zina for getting a little (or a lot!) scared when the teacher suggests that she, herself, might be suspected (18.15-18) so the whole Queen Bee act only gets her so far.