I believe the box must have landed on her leg. Our Margaret lived and she is doing great - although she has a limp. I am keeping her in a brooder in my house for the next week or so and giving her arnica to see if her leg heals. I had another chicken; a curious, high flying Wyandotte that injured her leg and it never did get better - so I guess we will just see. But I am so thankful she is still with us. Thank you all for your help.
That is great news! And I bet you're perfectly fine too, with the exception of a few grey hairs! Seriously, so happy your hen is doing well. Thanks for the update.