We have two ferrets, Freddy and Sydney. Both are fixed and both are a little over three years old. The previous owners said they were from Marshalls

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Last month I noticed that Sydney seemed to have lost some weight. I took her to the vet for a check up and he said she'd actually gained weight from the last time she had been there. He said she looked really good and not to worry about her.
I just noticed this evening that she has some hair loss on her tail and her private area seems to be swollen (though I can't be too certain, I don't make a habit of check that area out). We're taking her to the vet again tomorrow to have it checked out.
I was just wondering if this is possible adrenal disease?
And if it is, what can I expect? Is it curable? Is the surgery very expensive?
I'm not too worried about the cost. The vet we go to is always giving us breaks and lets is make payments.