My adopted gerbil has started scratching recently behind her ears. The cage has no signs of mites, and her ears don't look infected. I unfortunately can't hold her as she doesn't like it at all, due to the treatment from her last owner, so I can't get in and have a good look inside her fur. There's a tiny bald bit behind her ear. Not really sure what to do, because I have 2 other gerbils, who aren't scratching (not yet anyway!) Is there anything harmless this could be due to? Like dust or an allergy of some sort? Could she have mites even if I can't see anything in her cage or fur?

I would appreciate so much if someone could help me before my house becomes infested with mites!