Impacted gizzard is very difficult to diagnose until necropsy. Sometimes, if it's caused by a foreign object, it might show up on x ray depending on what the material was made of. There is no way to feel it or see what is actually causing a back up there. Sometimes eating a lot of fiberous material can cause a gizzard impaction if it's just too much for the gizzard to handle, or if they don't have access to proper grit. In a 5 year old hen many things can cause digestion to slow or stop. Since capillaria was found in the fecal float, I would try to treat for that first. Reproductive problems like cancers and infections can also slow or stop digestion. And parasites can also do it if there is a heavy load. My only gizzard impaction was a bird whose crop would not empty no matter what I tried. I spent 2 weeks trying. She was becoming emaciated so I euthanized. On necropsy all her organs looked normal and unremarkable, but her gizzard was crammed full of food and grit, nothing that would seem to cause a blockage, but her gizzard did not seem to be a normal size, looked smaller than I expected and there was a small kink in the proventriculus. There was nothing in her digestive tract past the gizzard, completely clean and empty. She had only been passing clear fluids with a bit of urates. So suspect it was maybe a congential deformity and it just stopped working properly. There is a disease called PDD which affects the proventriculus, but I think it's pretty rare in chickens, and it often has neurological symptoms which my bird did not have. And I've not seen a similar gizzard in any of my other birds. Outwardly, except for the crop stasis, she appeared normal and healthy, and continued to try to eat voraciously.
I wonder if your hen, if she's molting again like last time, may be ingesting a lot of feathers which could cause a problem if there were too many at once. Make sure they have access to appropriate grit all the time in a separate feeder. Or the timing could just be coincidence, and it's a completely separate cause this time. I would treat what you know for sure, the parasites, and then go from there.