So sorry for your loss. I think your hen may have had cancer. It may have been in her reproductive tract, or she could have had liver disease, which can be secondary to reproductive infection. Fatty liver disease could have caused bleeding. Yellow poop can be egg yolk peritonitis. It is all just a guess without a necropsy. You can try and do one yourself, opening her abdomen to look at organs, taking pictures to post here. Or you could refrigerate her body (don’t freeze) to take her body or ship it to your state vet for a necropsy and diagnosis. We can help with pictures of necropsies if you do one.