You can get Ivermectin at some pet supply stores. Make sure it is HORSE ivermectin -- it is much better than Ivermectin for dogs. However, I'd make sure it was actually mites before using it. Ivermectin isn't somethign to be fooled around with. Check her fur and see if you can see anything. If she is the only one in the litter with a bald spot, I would suspect barbering rather than mites or lice.