I have a 3 year mixed breed named Sweetnums I also have her sister Lady. I loved them both dearly. For some time now sweetnums had this scab on her back that doesn't go away it doesn't bother her at all. I don't think she even notice it, but I sure as heck do. It was a big scab, but than one day I notice it was gone and I could see the wound. It wasn't red or anything just looked old and had some dead skin around it. Later a scab return over it, but still it hasn't gone away. A bit of a history on her is that her Mom had very sensitive skin ad even flee allergy. Sweetums has the same. Just not as her mom.

What does the vet say about it?

Take her to the vet. Our dog had some skin issues and the vet was able to diagnose it with an exam. We were given a shampoo plus meds. We can't do an exam here. Your dog deserves to be taken care of properly.