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If your vet is calling them sebaceous cysts, then there is very little you can do to alter them. It does sound like hers are more serious, and you deal with a problem more often than others.
It is never a bad idea to see a dermatologist--dog specialists are readily available these days, but there is no guarantee they will have a different answer. I've not ever found these to be dietary or environmentally related, but something else may be going on with her that predisposes her to these.
You can try a different diet, or try frequent bathing with one of the benzoyl peroxide or chlorhexidine shampoos. They may not help, but they'll do no harm.
He may mean apocrine glands then, but these may also respond well to the special shampoos. I'd probably lean more toward the chlorhexidine choice.
Your best bet to find a dermatologist locally is to find a 24 hour emergency hospital, and see if they can give you more information. They most often know the closest ones to you, but there may not be one close.
If not, talk to your vet about special diets and about the special shampoos. These should be readily available.