Could she have eaten something toxic? Or possibly drank stagnant water?
I think this is the next thing to rule out.
If she is pooping, I'd guess that it's not an impaction. Brown and runny doesn't sound abnormal
I assume it's not possible for an animal to have gotten hold of her? Is it possible that a drake was overly rough with her?
In the event of poisoning, I'd reccomend giving her activated charcoal, you could give her 1g per kg of body weight, mix it with enough water to become a liquid, but not too much that she can't stomach it. It can be administered orally but you would have to be very careful.
You'd use a syringe and you'd push it to the right side of her throat avoiding her glottis (airways). You may need two people, one to hold her, one to syringe.
The black circle in this image shows where the liquid must go down, a bit past the glottis
View attachment 4192233
With her tail down, I'm wondering if she may be having a hard time laying an egg. If she is pooping, she must be drinking some amount, and isn't likely egg bound. But they can have troubles with the egg while it is higher in their system, to be absolutely safe and rule it out:
Give her 1ml of calcium gluconate (durvet brand) from TSC. Orally over a treat, or syringe fed the same as above directions.
Or give her a 600mg calcium citrate tablet. You can pop it into the throat if youre careful, it would need to go into her right side, the same again as the image directs.
Try feeding her something really tasty and see if she gets her appetite back, like blueberries, banana, mealworms in a bowl of water or peas... whatever she usually goes for. If she would eat it, plain scrambled or raw egg would be excellent for her, full of vitamins and protein. Make sure she has constant access to clean drinking water and grit.