Something's wrong with my gerbils tail....?

So I was holding her in my hand today and petting her. I felt her tail and when I got to the end tip of it, it felt rough. This was new because I hadn't noticed it before. She seems to be loosing hair there, and as I remember it used to be quite full of fur. It has scabs and looks like there's holes, like bite marks perhaps? She has black skin so I couldn't really tell. And she wouldn't sit still so it was challenging to examine. I suspected mites or ringworm? What ISS wrong with her? And what do I do to treat it? (please don't say call your vet, because my mom won't let me. She doesn't think it's worth the expenses)