Sometimes just the body's stress of making those first eggs is too much.
I suggest the poo being different is likely unrelated. We all obsess about the details when they die of something we didn't identify. I lost a duck when she was a year old and I never figured out why. I often go over the random things I recall about things at that time. Truth is I will never know, and this obsession stops me from moving on.
Do get a necropsy if you can, some states have a service to help with that. Or if you are brave enough to do it yourself, others here can help you if you post pictures.
Please don't beat yourself up. You loved her, she had the best life you could provide, and so few creatures are so blessed as she was. We cannot make them immortal, no matter how much we try.
Love the others and spoil them in her memory.