Animal abuse of any kind should not be tolerated in any form nor should their be any excuses for it either. If you can open the eyes of the person, regardless of age so they won't repeat it, then that is even better. If this person is old enough to get curt and say several times not to lecture her, it is apparent that they knew it was wrong yet let it happen anyway. They had a way to end the suffering of that hen, unfortunately the adult in this situation didn't take the initiative and do the right think and then educate the child on what they did. It wasn't her or her family who was suffering, it was an animal.
Too many times on this board many of us see the above happen time and time again. One can hope that they see, as I stated, we are animals caretakers and in that, should be more serious in our care of those animals. A swift death, as good of care as we can possibly give, the basics of a first aide case close at hand or in our barn in case we should need it, and the basic knowledge and understanding of what to do should something happen. In my barn I have a first aide book for horses in case I ever need it, and have I had to use it? Absolutely. I have basic first aide bandages, salves, band aides, sprays, and some holistic medications as well in the cabinet should the need arise for them as well. I don't think I was hard on the OP at all, as if you think I was, ask my 16 year old son how I was when I realized he wasn't feeding our field mouse Tiny and she almost died while in his care.
I ask everyone, please, show a little more compassion to ALL animals. Take their general well being a bit more to heart, be then domestic or wild.