Hi Kim - that's EXACTLY how my two year old Black Sex Link gets about every two to three months. I use a needle/syringe and drain the watery fluid from the "balloon" and she's good to go for another two to three months. She will feel so much better if you get that pressure off her. Just insert a needle in bottom of bag that's hanging down. There are no vital organs there and you can't hurt her. If you can't draw out any fluid, pick another spot. I'm betting she's full of fluid. Could also be an internal layer but it doesn't hurt to try a syringe first.
Best of luck. My hen has been filling with fluid (Ascites) for several months. I now watch and drain her before she gets too big. But she lays an egg every day so I know she's not an internal layer.
Best of luck. My hen has been filling with fluid (Ascites) for several months. I now watch and drain her before she gets too big. But she lays an egg every day so I know she's not an internal layer.