Most feed stores carry a powdered probiotic for livestock. I know for chickens you can give them good quality plain yogurt but not sure a duck will eat yogurt. So check with your feed store or TSC. You want to put back the good bacteria that the antibiotic killed along with the bad. How is she...
I'm thinking you need to get her on an antibiotic asap. heat means infection big time. I am thinking haunted 55 said she has hers on Duramycin I'll see if she is available...