Help

Hey reddit you helped me before months ago when I first adopted some for lack of a better term abandoned chicks. Up until tonight they've done amazing laying good eggs living and super friendly. I won't include pictures unless someone more knowledgeable requests but tonight when putting my birds to bed I noticed I was missing a hen. After about two hours of looking in the fields my dog found her. She had been dead for at least a few hours and I have zero idea why she was so far out by herself. She hadn't shown any signs of predation or bullying that I could tell but without being to graphic it looked like her insides had literally fallen out. I left my one dog to guard the body while I went back to get a firearm and my other dog (both are well trained and protect the flock and can handle themselves if a predator were to show up) upon double checking I wasn't able to find any tracks blood trails and again apologies all her organs were still present. So I'm almost certain it wasn't predation. My question would be has anyone else ever experienced this? Should I check my other birds now for some super virus? I'm legitimately heart broken never would of thought a bird could have me this messed up. Any help advice anything would be appreciated.