Environment is a huge huge factor when it comes to chickens. I moved my light Sussex and white Orpington to a new home a couple of years ago (custody battle with the ex, haha) and there was one soft shell egg + one no shell egg directly under the roost that very night - Like the change rattled the eggs out before they were ready - Then neither of them lay for about a week until they'd settled in. Chickens are very social, sensitive, and big fans of habit. Change something up or introduce a factor that's stressful and they will more than likely stop laying. That being said, the other side is that if change something up in a way that makes them feel happy and safe, they'll show it by being their cheery charming selves and laying as they should. I remember my dad once found an ad in the paper, 'free - 4 old hens, finished laying' that he just couldn't ignore because it made him sad (haha, he's a sweet man like that), so he took them in and doted on them... Lo and behold, these old hens who'd 'finished laying' went on to lay for another few years until they died of old age, because they were happy and healthy felt safe in a home where they were treated right

I don't think there's any definitive answer as to when hens stop laying; it varies so much by breed, individual genetics, flock and home dynamics, stress levels, health, environment, weather, quality of life, etcetcetc... In fact I'm not convinced that all hens necessarily ever fully *stop* laying, maybe it slows down a lot and becomes quite sporadic with age, but if they're happy and healthy they often continue to lay at least the odd egg here and there for their entire lives. Sounds like your ol' girl is feeling a lot better, congrats on your happy home and yay for getting eggs again
