You can act like a mother hen and give her a gentle corrective 'peck' (or gently push her beak away, or something similar) to alert her that that isn't okay.....but if you are to do that, do it now before it is too late!
I bet
@Shadrach would have a technique on how to do this. I have seen mother hens peck their chicks when they were being a bit 'aggressive', but not sure at what age that started. And, mother hens can talk to their chicks to alert them to okay or not okay behaviors. An unhappy squawk, a content purr, a tidbitting sound, etc. Whatever it is, it shouldn't actually hurt them...and the 'message' should be consistent EVERY time they peck, so they learn it/associate it appropriately.
Maybe a gentle push of beak away and an unhappy squawk sound paired???