it's important that the broody hen is taken away from the nest box to eat, drink, "go" and exercise the legs...and/or put food and vitamin water away from the nest so she has to get up and walk to it.
some hens will sit too long and must be picked up.
check for mites.
describe the droppings..color and consistency
has she been wormed?
do you have poultry or chick vitamins?
try and get some Poly-vi-sol liquid baby vitamins, Enfamil brand if possible, no iron..
give 3 drops on beak once a day for 4 days..
then 2 drops for 3 days..
then taper off for another for another week.
make up this mix..
this is for 3 feeds for 1 day..give for 5 days along with regular feed and water..
1 cooked chopped egg yolk
1/2 teaspoon honey or unsweetened applesauce
2 tablespoons plain yogurt
3-4 tablespoons water soaked or cooked oatmeal.
add enough layer feed to make mix puffy, not soupy.
help the hen by getting her up on her feet and helping her to stand.
you might try a little "therapy"..by gently moving the legs a few times a day.
hope she gets ok.