[cypher]

It is a bit baffling, I agree the food is unlikely to be a problem, mites seem highly unlikely too, so many people seem to use that sand I wouldn't have thought that would be a problem either but you never know really.
What food was she on before, just wondering how big a change it's been although I do doubt that's the issue.
As it's a small isolated patch allergy seems unlikely too.
A bit of a random guess but iis it possible she may have had a small cut from something & been scratching at it as it heals?
It might be worth just giving her some extra linseeds & some EPO while you try to figure it out, it may help & certainly won't do any harm.