Two possibilities come to mind. Either she has an impacted crop in which case gentle massage of her crop may help, or she is egg bound and her digestive tract is stopped back up to her crop. Have you checked her vent for a stuck egg by gently inserting a lubricated gloved finger and inch or two at most into her vent. If she is egg bound you should be able to feel an egg pretty close inside, perhaps slightly above. Beware she may poop when you remove your finger, so make sure she is on a thick old towel if you do it with her on your lap. If it is a stuck egg, a calcium tablet like human calcium with vitamin D or a Tums indigestion tablet may help but if she is badly stopped back, the chances are her body will be unable to process it and a warm 20 min soak in an Epsom salts bath and lubricate her vent with whatever you have that is appropriate.... KY jelly or similar or coconut oil etc. then dry her feathers thoroughly with a towel and hair drier and place her in a box with clean nesting material and good ventilation somewhere warm and dark.... a heat pad may help her.
If it is a straightforward crop impaction and her crop is really full, it may be best to empty some of the fluid out by gently holding her upside down by tilting her forwards and slightly to her right and massaging her crop. I usually hold them against my chest and tip my whole body forwards so that they are supported and I can monitor them closely and stand up to give them a break when they need it. The reason for tipping forward and to the right is that the oesophagus is on the right side of the mouth, so there is less likelihood of the bird aspirating vomit into their trachea if the oesophagus is the lowest point. Be aware that vomiting a chicken is risky because of the potential for aspiration but if you massage a crop that is already full without first vomiting, there is the possibility of the fluid refluxing into the birds mouth and them aspirating anyway.
An impaction of the crop is often caused by the bird ingesting strands of long fibrous material like grass, hay or straw, but it can also be caused by a foreign object or even a large lump of food getting stuck.
Let us know how you get on and if you are able to identify if the blockage is at one end or the other. Good luck!