I have an Amber Star hybrid which laid normally for her first year, then stopped last Autumn, and hasn't laid since. Mine still crouches when I approach, and hasn't crowed or made much noise, but she has developed a very large red comb and has always been the top hen, though not aggressively so. I put mine down to some hormonal imbalance which has developed, as otherwise she's the picture of health. I keep her on because she's best friends with my other hybrid, who is a really good layer!
With yours, so long as she seems otherwise OK I wouldn't worry, just wait a bit and see how she gets on. Certainly less worrying than the usual egglaying or prolapse problems with hens over 3 years old. Many hens slow down or stop temporarily round about this time of year, and she may well be getting ready for a moult.