Why is Root so angry with Holly at the end of Chapter 3?

Root is angry that she went against his orders to hang back. He had told her that she did not have a human invitation to enter the sight. Holly stretched the rule and used a baby's cry as an invitation. She explains this to Root who accepts it, but he is still angry. Then a human is spotted who has not been knocked unconscious by Holly. Root calls for everyone to shield themselves, but Holly can't. It turns out the human is just a toddler, so the problem does not escalate, but Holly is commanded to get her powers before returning underground.