I agree that it takes a while to learn. My 7yo never had a pet until we got our chickens this summer. He terrorized them, chasing them because I guess it's both fun to see them run, and to have that power which a 7yo doesn't have anywhere else. I kept at him, letting the chickens take refuge on my lap, and it finally sunk in that it might be more fun to have them as playmates, rather than hiding under the deck. Now, they run to him because he digs holes for them to scratch in, and possibly dust bathe in.
Kids need time to learn, and the maturity to process what they learn. Your daughter is likely traumatized, never having imagined that her favorite hen could die and be gone forever. She will learn, and be fine.
Accidents happen. No one is to blame.