Good morning to you...you have certainly posed a unique question!
First, are your dog's ears upright or floppy? I know it seems silly, but I am trying to visualize whether you are describing sores on the skin below her ear canal or sores on the tips of her ear flaps...
How long did you try a different food? If your pet has any type of food allergies, you will need to leave your dog on the new food for at least 8-10 weeks before knowing whether or not it is helping.
Is your dog itchy overall?
Is the problem getting worse or staying the same?
Unfortunately, I don't have an answer that won't involve more testing...your veterinarian might even recommend a referral to a veterinary dermatologist. I know you might not want to spend some more money, but I really think the only way you might get some answers is to have more diagnostic tests run (allergy testings, skin scrapings, cultures for bacterial infection or fungal infections, etc).
Let us hear from you..
Tomcat
Is it really cold where you live?
Our dog got frostbite on the tips of his ears once and it looked like little black sores (almost specks) that would crack and bleed at times. It was very, very stubborn to treat. The tips of his ears were sensitive and had problems for several months.
I cut open vitamin E capsules and put that on it with a generous coat of Aquaphor twice a day until it healed (vaseline or another ointment might work as well though). It did eventually heal completely.
I hate to butt in on someone else's question but I will do it anyway... My Boxer also has small sores on the tips of his ears. He also has a small sore on his forehead. It starts out as flaky skin then develops into red almost bleeding scabs, to the point where small notches are missing off his ears. He's had this condition since I picked him up as a puppy (one year ago). He has floppy ears not cropped. I used to have a dog that had Lupas. I hope it's not that again!
Thanks, Stacey