Here's how to tell if your hamster has mites...
Take Luna out of her cage and put her over a paper towl. Take a comb and brush it through her fur. Then take a magnifying glass and check to see what came out of her fur on the paper towl. If it mites then bleach her cage and everything in it. (Make sure you dilute the bleach) Then take her to the vet again and ask for something for mites. If she doesn't have mites then just go back to the vet anyway to tell them that your hammy isn't getting better.
I hope I helped
I'm not an expert in these things but i researched this on the web
Good luck with Luna!!