I wish I could say there was improvement but this is what she looked like as of last night.
The only good news is that her labored breathing seems to have slowed and she seems more comfortable. She still looks absolutely awful.
Now it looks more like ich to me, but if it's ich, it's the most severe case I have ever seen. I'm convinced it's some kind of ectoparasite/protozoan like ich or velvet because columnaris usually looks like a bacterial infection with slime coat bunching up and sloughing off, and this is obviously not that.
Regardless of ich or velvet, the copper should be working on it, and the salt especially should be helping if it's ich. Maybe I'm just being impatient. Today was day 5 of the copper. I don't know how long it usually takes to look better. There's an impatient part of me that wants to remove the copper and do a salt dip or a potassium permanganate bath, but I'm trying to tell myself to wait and let the copper do its job (let's hope it does).
Oddly, the other three fish don't even look to have anything on them. If they do it's not noticeable. I'll have to flashlight them later when they're sleeping and see if I can see anything.