Kfry, well, that's about what I expected. You're right, it's well and truly gone. LittleBettas is right, it can get very easily infected. I'm not sure this girl will be able to go into a sorority with her gill like that. :/ But she looks very good otherwise, nothing is clamped and she looks happy. But I do worry about potential infection.
Okay then, if I add her later do I have to change everything around? That's kinda hard in a planted tank. Anyways, I guess maybe I will have to put her bigger cup in the 2.5g until she is healed up. How long could that take to heal up? Just asking for like an estimate.
It's good that I got her though I am pretty sure if someone got her, they wouldn't know what to do.
I'm not sure if gill flaps ever grow back. I've only seen pics in my fish disease books and that particular fish had er, passed on. If it does grow back, I would estimate at least two months or more. But if it doesn't . . . well, you could put her in the sorority but it would definitely mean an increased risk of infection for her.
I've forgotten the conditioner before too. In my case, it was during my great tank teardown where I switched substrates in my 20g. I forgot to put the conditioner in the holding tank. :( 3 rummynose tetras and 5 neons died, some within a half hour. I still feel bad.
I'd say give her at least a week off of the AQ salt but keep with the Stress Coat (don't be afraid to put extra in). That's pretty cool it's starting to grow back.
Is she in the 5g? With one fish and as long as you don't leave uneaten food, she can get by with 1 100%. But with her gill exposed like that, 1 50% and 1 100% a week would be better. Or even 2 50%. But just this once, she should be okay.