Chicken got really sick one night then died in morning. why?

[jkp11]

She was fine when i opened the chicken coop in the morning, but when I went down to shut it she was on the ground. She was breathing rather hard and raspy. Also i noticed she had a lot of white discharge from her vent, but when someone looked at her they said it was not egg binding. she was alert also so i have no idea what happened. it also happened so fast. any thoughts?

 

[TwoCrows]

I am sorry for your loss. I don't know why she may have died. Maybe some one else will come along and give some idea.