Roxy - the egg tract issue I mentioned - I really can't tell you much. When young/new layers lay a soft shelled or jello egg, it's generally just the egg organs working the kinks out. But when those same issues happen with older birds, we become more concerned. If it's just every once in a blue moon, no big deal...just put down to a fluke. But as humans can become sterile due to various organ issues, so can chickens and other animals. Because your girl hasn't laid since summer (when days were still long), I'd suspect a permanent problem with her i"nternal lady parts"...lol. If she's just a pet, not a big deal. Folks who want layers primarily for eggs would probably put her in the stew pot. But who knows, maybe she'll resume in the spring???
mcj - sorry about your chicken issues... Depending on how many hens you have, going from 3 eggs to 1 egg a day is not bad for this time of year. Between molting hens and the short days (I don't supplement light), my four LF girls are only giving me one big egg a day. Thankfully my little bantam girls are still going strong...