50/50 water and rubbing alcohol. Do not feed her foods with yeast in them. The dog food can even be the problem. Depending on how bad it is you may want to take her to the vet. My dog had the same issues and the vet told me to use the rubbing alcohol and water. Good Luck!
I would take her to a vet. They will give you antibacterial medication and a wash for her ears. Your vet can also give you advice on keeping her ears infection-free, such as keeping her ears clear of excessive hair.