Hi , I'm James DVM MRCVS and would like to help you with your question
Sorry to Hear about Frida being uncomfortabel
by the symptoms you are describing , one of the first things that come to mind are indeed being - egg bound.
if that is the situation that I would strongly recommend visiting your vet as he would be able to asses Frida . at times mild sedation would be necessary in order to diagnose the condition (performing an Xray) and then ever so gently manipulating the egg into coming out .
It could be that the egg of very large will require to be taken into piece by first draining it's constant by a syringe . this is something that must be done by the vet though, and not at home.
if you are insisting on trying at home .
try to see if you can feel a large bulge in the pelvic area gently massaging it (only if she is not too stressed by you doing it)
Apply some lubricant to the area to help the egg exit easier and give her a nice warm area to relax for a while. If she is used to being handled and doesn’t find it too stressful then submerging her bottom area in warm water and gently massaging the area for about 30 minutes may help relax the muscles. An alternative to that would be a warm flannel held over the area. She needs to be kept warm and comfortable.
If could be that it being egg bound is not her problem and we are dealing with something completely different such as a parasitical or other infectious agent which might be effecting her (though does not come high up on my list at this point as your other hens have showed not symptoms similar to hers) .
I would suggested starting with the advice I have written down and take it from there.
I hope this helps and if your have any more questions on the matter , please contact me .