PLease don't beat yourself up!!! Stuff happens. You can't always be there!! You were being a good Mommie and that is even more important. That picture looks awful. I am absolutely no expert and i have never dealt with anything like that but I have to wonder if it isn't an abscess of some kind to swell so quickly. I am not sure there is anything you could have done even if you found her right away!!! I am very sorry if you did have to cull her, but she does look in pain! I am dealing with an injured bird too(fox bite) and trying to decide if I should give him a chance to heal or put him out of his misery... I truly understand. Good luck! Hope you children are feeling better and you stay healthy!!!!