Dog has smelly/over active anal glands!?

I have a female (fixed) golden retriever/maybe irish setter mix, about two years old. She has a very strong anal gland odor, I empitied them once externally and they were very full but i used some pretty firm pressure. She goes a while without stinking but if she has any supplements and certain foods make them act up again. I feed her Natural Balance Lamb and Brown Rice L.I.D. So good food, also, I have been giving her a prune once a day- whole wheat bread if i want to. I gave her raw chicken as treat but i don't give her anything else really. Why is she so stinky??!! I don't know how to keep this from being so gross- i have read to try your best to get the glands to express on their own, it may cause more harm than good to express them yourself too often.