Has your vet done skin scrapings on her? I'm assuming thats the first thing they would have done. If your vet is choosing not to treat with Ivermectin due to a clean skin scraping it may be wise to have another one done just to be sure.
But I agree with Dog Dancer, the best thing to do is to find out precisely why the vet has chosen not to treat with Ivermectin.
P.S. In my experience Ivermectin has always been most effective injected. I don't think orally dosing her would be the best option. But again, contact your vet for a more in depth reason for his/her decision and perhaps ask if there would be any harm in trying the treatment.