Thanks for writing in,
Has your vet done an otoscopic exam where they look into the ear canal?
Has your vet done an ear cytology to determine if this is a bacterial or a yeast infection?
What food are you feeding her?
Is she itchy anywhere else?
Ok, Thanks for that added info. Well the first thing here is to have a cytology done on that ear so we know what we are dealing with. Is it bacteria, yeast or both? This will help determine what you need to clean and treat with. If it is a yeast infection that just keeps recurring then your vet should give you a cleaner such as Dermapets' malacetic otic which is great for dogs with this condition. I would also suggest an otoscopic exam be done to ensure there isn't a foreign body in the ear canal. This is fairly common and could help to explain why the problem in one ear and not both.
Your dog definitely sounds like she has allergies. You may want to put her on a food trial for food allergies. This would require an 8 week trial of a dog food with a protein source she has never been exposed to before such as duck, venison, or kangaroo. These diets are only available through your vet. She may also have inhaled allergies (esp. in the summer), in which case she should be allergy tested or started on a product called Atopica which is great for dogs like yours with inhaled allergies. I hope this helps to give you some guidance for your girl. Let me know if you have any further questions.
Dog Veterinarian
Veterinarian, Dog/Cat Veterinarian