I'm not sure, I do have never had a bird get bullied enough to starve. Some other illness or maybe even the weather could have made her go off feed. What are the temps by you? I have several young chickens go off feed because of the cold. I don't really know how she died or what she died from...
Nope, not blackhead. It will take a turkey 7-14 days to start showing any symptoms after being infected. Blackhead can take over a week to kill an adult bird and definitely can not kill a mature hen overnight. That poop does not really look like it is the result of blackhead either, infected...