Assuming your bird's sinuses are still swollen, have you tried Terramycin opthalmic ointment? I found out after I gave a hen away (to someone that said his dad knew how to treat a long term sinus bump) that you have to massage around the eye for several minutes after you put in the drop or gel. This should happen twice a day, minimum. Once the tear duct absorbs the medicine, it should end up in the sinus cavity where it can fight the infection. However, since giving away that hen around 6 years ago, I've treated some doozy sinus bumps, not all successfully. The worst ones resulted from wet pox, and nothing I did cleared those viral eye infections. Chicks died. I came tonight to find an alternative treatment to Terramycin for a friend's Leghorn hen.
History: hen had a long-term sinus bump so big that the eye was hidden under the swollen tissue. The friend can't afford a veterinarian, so I suggested she contact a local chicken rescuer whose knowledge impressed me when I heard her teach at a chicken show. The rescuer cut open the facial bump and dug out the hard pus. Sad to say, my friend's rooster died a few days following his facial surgery. The hen's bump came right back. Since infection resisted terramycin ointment applications, I suggested my friend try injecting oxytetracycline LA with a tiny needle for diabetic insulin injections. Facial surgery and/or injections are not something to try unless nothing else works because the face has a lot of nerves and bleeds a lot.
I am now chicken-sitting while the hen's owner is visiting relatives. If a tiny test spot bleeds, I don't inject there. I find another spot close to center of swelling. Then I inject a second spot. So far, each injection has liquified some pus so it came out of the hen's eye and slit in roof of mouth. I also use a cotton swab to put triple antibiotic in the slit in the roof of the hen's mouth--carefully; it makes her gag. I also rub triple antibiotic around the facial swelling over a long period, like 15 minutes. After 4 days, I can see the eye, barely. I wondered about switching to enrofloxacin aka Baytril injections, which should not be used on chicks or juveniles due to side effects such as deformed joints and sudden/permanent nerve damage, etc. Tonight's reading on BYC suggested Ciprofloxacin Hydrochloride opthalmic drops, so I'm going to ask my vet about getting some. I already bought children's immune gummies containing C, D, and Zinc, and started giving that to the hen to see if I can build her immunity. I also give her probiotics in her feed because antibiotics do such damage to normal flora that it can take months to rebuild otherwise.
I am not trying to discourage you. Your hen's sinus swelling sounds like an easy case compared to most I've treated. Mycoplasma is a common culprit in the south, and CRD is what happens when other pathogens get involved. You can usually tell by the smell. If there's no odor, it might take a lot of effort to find a treatment that works. I don't know of a virus that would cause swelling over such a long time. If your hen has allergies, no amount of antibiotics will help. Nasal spray with steroids might help along with anti-inflammatory essential oils such as lemon in her water. There's a lot of good unbiased research now available online concerning natural substances that fight infections and/or boost immunity.
I try to read at least one study every week to have a fighting chance at keeping my chickens healthy. Either that, or BYC. You just have to be careful about old threads that suggest culling an entire flock. Not practical for CRD according to Dr. Gary Butcher, U of F Poultry Specialist. Not an exact quote, but he said every commercial flock and close to 100% of the wild bird population in the south has mycoplasma, and if any standard antibiotics would cure it, the commercial industry would be free of the disease by now. So I keep reading research...