I would order a used copy of a good chicken book online which can give you a lot of details about chickens. Storys Guide to Chickens is an okay one. You can bet a ton of info here, but it can be subjective. We have learning center pages written by members. The emergency forum and other forums are a great place to search.
Lifespan varies with chickens. Some can live 8-10 years and rarely older, but after 2-3 years, it can be common to lose a chicken now and then to reproductive disorders, such as salpingitis, cancer, and others. You can always save a body, keeping it cool, and send it into the state vet lab for a necropsy to find out exactly what the problem was. Many of us do a basic necropsy at home, which can help if it is an obvious problem, but the best are done by the poultry vets.
I would glove up and insert a finger inside her vent to feel for a stuck egg. Bring her inside in a basket or dog crate if it is safe, get her warm, and offer food and water. She could be dehydrated from not being able to stand. Electrolytes (pedialyte or gatorade) or the chicken kind are helpful.