You have two health issues going on here. One is the white crust on the face of the broody, the other is a broody that's been broody too long. So let's get some more information so we can all help.
First, go take some photos of the crust and post them here. It's easy. Select "full image" as you are posting the photo.
And tell us if she has chicks.
Second, the broody likely needs to be broken to end her compulsion to stay on a nest where it is now affecting her health. This involves an open mesh bottom cage so air can flow under her day and night for a few days. If she is not brooding chicks that have hatched a week ago, this will be easy. If she has chicks, we'll deal with that.
As for the crust, have you inspected the inside of her mouth and throat with a good light? This will help is figure out what this is.