Sorry for your loss. I think you did all you could for her in this short amount of time. It’s tough to say what the issue was without knowing a little more about her, such as when her last egg was laid.
From the pictures it looks like she did get picked on or over mated pretty badly, so she could’ve been weak from being kept from food and water. In this case, isolating her with her own food and water, as you did, would be good.
Her abdomen (between her legs) looks like it might be distended, she may have been suffering from a reproductive disorder. In that situation there isn’t a whole lot to do. Sometimes a course of antibiotics can help, but they may only buy her a few month of relief. Sometimes draining the abdomen may help, but it can be risky. Crop issues can go hand in hand with reproductive disorders, which is what may have been going on with her.
Upon initial inspection always check for lice/mites, listen to breathing for any wheezing or rattling, check the eyes, ears, nose, mouth for any discharge or lesions, then the crop first thing in the morning; it should be flat. It’s also helpful to know when her last egg was.
