Anal gland issues are often the cause of a dog spinning on their rear end, but there are other causes such as tapeworms or allergies.
Tapeworms release segments that exit the anus and spread tapeworm eggs into the environment. They can cause severe itching in some dogs. They can usually be seen in the stool and are small about 1/2 inch moving things. If the stool has dried, they look like rice in the stool or stuck in the hair around the anus. Drontal plus is also a prescription product and is used for the treatment of Tapeworms, though dewormers with praziquantel work well against tapeworms.
The last is allergic condition -- flea allergy being the most common allergy leading to itching around the base of the tail and rectal region. If your dog is not on flea preventative then this might be the problem. Benadryl at a dosage of up to 2mg a pound every 8 hours can help with any symptoms related to allergies like itchiness.
A Perianal Adenoma is also a possibility. You can read about this here:
If she was my dog, I'd try the benadryl to see if that relieves her itchiness. If she continues, I'd deworm her for tapeworms and see if that helps. If nothing helps, then you will need to have your vet take a look at her.
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