Welcome, you have come to the right place. I went through a crisis with my hen a week ago and the people here were very helpful.
Is her crop full first thing in the morning?
My hen was egg bound. This prevented her from pooping and so food could not move through her system. What I did was to do a cloacal exam which revealed an egg that was stuck. I put on rubber gloves applied astro glide, ky jelly also works, and gently inserted my index finger into her vent where I could feel the egg. I put more lube and worked it around the egg, gently, you don't want to crack the egg. Then I took small piece of a tums and crushed it and added water and gave it to her with a dropper. The calcium causes the contractions that will help her to lay the stuck egg. Within 15 minutes she laid the egg. It could take up to an hour. If that didn't work they told me to soak her bottom in warm water. Towel her off well after so she doesn't get a chill.
I am sure others here will be more able to tell what is wrong with your girl.