Female getting kicked out

[TeenDuckLady]

2 females and 2 males swmiming in the pond. They've been together since September, but they've started biting one female. They don't let her swim with them, and she spends a lot of time alone. What is the problem??

 

[Miss Lydia]

2 females and 2 males swmiming in the pond. They've been together since September, but they've started biting one female. They don't let her swim with them, and she spends a lot of time alone. What is the problem??

For now I'd separate her from the others but where they can all still see each other or if the other female doesn't pick on her maybe put her sister in with her in their own pen and observe the one being picked on maybe something is wrong with her they hide things so well from us but their own kind pick up on it. Get some poultry vitamins and add to their drinking water she maybe be run down and stressed from the bullying but you need to observe her closely is she eating what does her poop look like etc. Is the pond water stagnant or fresh. How is she acting other wise taking an interest in foraging or laying down alot?