Does your friend have a rheumatologist or a neurologist? Reason I ask is, they'll need an ANA and RF test to verify they have Rheumatoid Arthritis, otherwise it will simply fall into the gap of things that "mimic" that disease, and they wont' really get help.
Same with MS. You'll need a neurologist to verify that that's what's happening and give the diagnosis.
In lung scleroderma (scarring?) those heal over time, though it can be a very long time. My lung scars didn't heal for at least 5 years and even now I can get sensitive in the ribcage in the same spots.
Don't go to a doctor and start with "Long Covid" because they'll brush you off. Try to get the MS or RA diagnosis and work from there. That's just personal advice. I think people ignore ME/CFS and Long Covid and want patients to "just wait longer" and they'll magically "get better" soon. Which is BS.
Don't let anyone but a rheumatologist test your friend for "Fibromyalgia." That should be a diagnosis of exclusion after RA is also excluded. A pain doc or a GP can't exclude RA definitely. I've been down that road.
As for what to do, this is all personal advice I'm not a doctor. YMMV
I'm recommending a general set of antioxidants. As much as you want your friend to be out of pain and suffering now, try to get them diagnosed first, before using heavy doses of antioxidants. Or it can mess with lab tests.
A general multivitamin with minerals, everyone recovering from anything should take this. We feel tired and we don't eat right and then our nutrients get out of whack and we feel worse. Don't take that risk.
Reservatrol and 2000-6000 mg of Vitamin C per day are a powerful combination for reducing systemic inflammation. But do that after you get the diagnosis. Glutathione is also available in pill form.
You should be aware that NAC (N-acetyl-cysteine) was studied for Covid exactly for the reason of reducing cytokine storm effects. Here's just one clinical trial
https://clinicaltrials.gov/ct2/show/record/NCT04419025 and that study references this site:
https://www.nacincovid.info/faq You could spend weeks digging up all the studies.
The FDA briefly pulled all NAC off the market during Covid probably because they wanted to make it a drug not a supplement. But that effort ended and it's back.
IMO, just take Glutathione, it's less likely to be banned and has the same effect. Don't believe any hype about things that are "better absorbed" than others. The only hype worth anything is independent lab testing and standardized formulations.
I hope your friend feels better and shakes off the Long Covid nightmare. 👍