Is something wrong with my chicken?
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There's several things that could be going on. Are flock members keeping her from food? Possibly doing a worming could help...though I am not a person that ever worms my chickens, but I know that advice is given here as an option.
Try scrambling some egg and feeding her away from the rest of the flock. Certainly if her egg shell is not strong she will benefit from more calcium. You could break up a calcium pill in her scrambled egg for a quick boost and then make sure she has access to oyster shell free choice.
I would add probiotic and vitamins to her water for a week also.
I agree with Bridebeliever on everything, separate her just long enough to give her something to eat of her own, the scrambled egg, add calcium to it, after she eats that you can see if she will eat regular layer food while away from the rest of the flock, fresh water is important. The watery poo is not necessarily normal but the white in the poo is normal. The poo could be watery from not having enough food, you said she is eating but not very much, that could cause the poo to be watery. If you don't want to use a worm medicine from the store you can feed her pumpkin seeds, they are a natural dewormer and perfectly safe and healthy for chickens. Other than that, I can only wish you luck in solving the issue.