Found it :)
Here is what Ron Kean has to say about vent gleet...he is an Extension Poultry Specialist at University of Wisconsin - Madison.
"If it is vent gleet, then a couple sprays of betadine should work. You should be able to find this at a pharmacy or from one of the mail- order vet supply houses. Vent gleet is basically a yeast infection. It likely can be transmitted to males that might be mating with the females. It only seems to occur in an occasional bird, though, so I suspect it may be more of a factor of some other stress that is involved."
-Backyard Pouthry, Volume 6, Number 2 April/May, 2011
He was answering a question from a woman who was told to spray hydrogen peroxide up the vent in order to cure the problem. So, by this answer I would have to assume that you spray the betadine into the vent area.
Hope this helps. If this is vent gleet, the antibiotics will more than likely make it worse. However, if she has another infection causing stress and making her susceptible to vent gleet then, she would need to be treated for both.
If it were me, I would probably stop the antibiotics..since, she wasn't acting ill...and treat for gleet. If that cures the problem then great. If she is still ill, at that point, I would continue the antibiotics.