Have you seen any lash eggs? Is her belly bloated below her vent? Take pictures of her poop constantly, and post regularly. I'll post another member, @coach723 , who along with @Wyorp Rock and @Eggcessive have seen this malady before.
Always take pics of her poop and post. What breed is she? What does she eat? Any changes in her comb? Does her abdomen look distended below the vent? Have you noticed any lash eggs?
I forgot to mention, that this study was done on white leghorns. In my reading at BYC, many, almost all, of the cases of salpingitis (reproductive related issues) were seen in hybrid chickens.
Post pics of the last eggs, especially the soft shell one. You need to start taking pics of her poop. One of the best diagnostic tools here on BYC. Post constantly. Does she have any yellowish discharge, or yellowish thick discharge in her poop? What color is her comb? What does she eat? What...
Please post pics of her poop. Is she lethargic? Does her comb look discolored, or droopy? Does she have any yellowish discharge? How is her appetite? Do you notice any swelling in her stomach below her vent?
I would guess from the symptoms you've described, and the up and down nature of her demeanor and health over the past month, and the swollen stomach, her comb color, that she died from salpingitis. You did all you could, as we all have done for our sick girls, but she probably had an incurable...
You should post pics of her poop, constantly. It's a diagnosis tool. Does she have any bloating below her vent? Has the color or condition of her comb changed? Is she lethargic?