I’m sorry about your hen. How is she doing? Just in initial appearances, you can see her face is quite swollen on the side with the lump. Is there any bad smell about her head? How are her eyes - any bubbles or discharge?
Inspect her ear on the side with the swelling very thoroughly; is it plugged up with gunk? It could be infected and that’s what’s leading to the swelling. If that is the case you will need to clean out anything plugging it up. Let us know if you see anything and we can help give you some tips on cleaning it out.
Another possibility is that this is an abscess. Is this a scab:
Did she get an injury that is infected perhaps? Or did something bite her, like a bug? How long has the swelling been going on?
Another possibility is some sort of tumor. Check all of the things mentioned above and report back with your findings.
Is her other side swollen at all? You mentioned it’s affecting her quality of life, how is she acting?
Also welcome to the site, sorry it is under these circumstances.