How old is your dog?Is she spayed?How long has she had this discharge?
I would talk to your vet about doing a culture and sensitivity on the discharge. This involves taking a sample of the discharge and spreading it on agar plates (petri dishes), then adding little antibiotic discs. In a couple days, you look at the dishes again, and use the antibiotics on the discs where nothing grew...
Unfortunately it sometimes takes a little bit before an effective antibiotic can be found that works, but don't get discouraged. The culture and sensitvity should take care of things.
ya I know that, I learned that in micro, but seeing as how I don't have agar, or antibiotic disc's I was asking your oppinion on a med, there are not a whole lot of species that produce a green discharge.
My opinion is that you need to have your vet do the culture and sensitivity.
Even if I had an opinion of which antibiotic to use, I wouldn't be able to give you a dose or even tell you what to use...as it's against the law to prescribe medication to an animal a vet doesn't have a personal relationship with.
Your girl could have a simple infection from swimming in the lake...however, she could also have a stump pyometra, which would require a whole different type of medication.