Hi, and welcome to FnF.

Can you fill out these questions to the best of your ability? They'll help us get a better idea of what could be occurring here.

Your description doesn't really sound like Flexibacter columnaris to me -- it usually appears as a wet-cotton-like fungus, often starting on the mouth or back/dorsum of the fish.

You may be describing increased slime coat, which appears grey or white and slimey, that can occur with water param problems, irritation, or external parasites, like velvet (using a flashlight to check can help). Velvet can also infest gills.

Has there been any aggression between her and the other fish in the tank?

~Ash