Well, it's sad news. Fishy died this afternoon, she was 3rd day of re-treatment - had looked quite bad since last night. Lots of fluff coming out of wound, and she obviously was not well, difficulty swimming about, not eating. Shame, as a few days ago she looked like she was making progress & was improving.
Anyway, dismantling quar tank now. All other fish in main tank still look fine, so infection had not spread to any of them from before she was moved to QT.
Thanks for all your advice & guidance anyway. Very sad, but at least the rest of the fish all look fine.