I am no expert on doing a necrospy.I too would like to know what actually killed her but knowing absolutely nothing about this, it felt overwhelming for me to try to do a necropsy on her. Is it as simple process?
My daughter and I both talked about it. I wish there was someone here that could help us. Having that big question mark makes it additionally heavy.
Surprisingly it is not too difficult if you are going to look in the abdomen and at the organs. The skin is quite thin, just like store bought chicken, it may be easier if you cover the head so you don't see the face.
With reproductive problems usually you will see that pretty obviously. Fluid, egg matter, sometimes an egg, etc. may actually be in the body cavity. Ovaries may be cancerous, etc.
If you do still have the body and want to try, take some photos we will take a look with you and give you our opinion.
Something I don't know if you have seen/read is the necropsy thread, it hasn't been active in a few months, but there are photos from BYC members and discussion of what is seen, you may find that helpful as well. The last 5 pages of that thread, if I remember correctly, most deal with reproductive problems. https://www.backyardchickens.com/th...ntains-graphic-necropsy-photos.823961/page-35
Again, I'm so sorry about Rosie.
Here's one necropsy manual.
https://vet.uga.edu/oldvpp/programs/afvet/attachments/how_to_necropsy_a_bird.pdf