It is hard to determine whether you're dealing with a fungal infection or a bacterial infection. Had you said it was cottony or fuzzy in appearance, it could still be both.
Anytime anything like this occurs in the "facial" area of a fish, I'm concerned about Columnaris, which is bacterial and requires broad spectrum antibiotic treatment. But, it's almost always fluffy and cottony in appearance, with red around the edges as it progresses, and it moves to the fins and tail and all along the body.
It's hit or miss all the time with these guys. If you don't see any improvement after a few days, it may be necessary to change treatments.
I would go with something stronger than Pimafix, though...It's a good preventative, but it sounds like this girl already has something going on.
Kim