There really is no way to know the cause of death without a necropsy.
Any signs of illness before death? - swollen abdomen, going off feed, lethargy, impacted crop, were all the eggs laid "normal" - no soft shell/shell less eggs or odd eggs found, any mite/lice infestation or worms, any odd egg yolk looking poop or signs of respiratory symptoms?
One possibility since she quit laying eggs would be an internal/reproductive disorder. Peritonitis, Salpingitis, cancer or tumors can be fairly common in egg layers, sometimes they can cause "sudden death", but normally you would notice the chicken going down hill for a couple of days.