I tried the beet pulp My herd queen, Sunshine is a Picky goat Regardless of stress or whatever and is the reason I finally switched to a pelleted feed so she would quit picking out certain things and leaving the rest that she Really needed.
 I don't recommend the beet pulp either. The sweet feed with Black Oil sunflower seeds(BOSS) is a good start. The BOSS has high protein, fats and selenium. Just a handful per goat is all that's needed usually.
 You make sure to mix the peppermint with a carrier oil. You can use plan old veggie oil if needed. It may burn if used straight. Most healthfood stores carry it and a little goes a long way.
 I hope you get it figured out soon.

there are some strains of mastitis that have become resistant to the today treatments, if that is what you are dealing with you will need to change to different antibiotic to get rid of it.  we have had some stubborn cases the last couple years that did much like what you described, the milk clears up after treatments but then it went bad again in just a few days, what i finally found that got rid of it was to make teat infusions with penicillin with some peppermint oil added to the infusion, given at each milking and continuing with it till 2 milkings past when the milk cleared up. the down side to doing this is there is no known time for how long residuals will be in the milk so if anyone is allergic to penicillin don't let them drink any of it for at least a month. you figure the dosage according to the does weight. the normal penicilin dose is 5 cc per 100 pounds, so if your goat weighs say 125 pounds that would be 6 cc, or 3 cc per teat infusion and just a few drops of peppermint essential oil added to that, you can also add some safflower or sesame oil to the mix to get a larger volume so it gets up in there better, that is what the 'tomarrow' dry mastits infusions are except they don't add pappermint oil and that seems to be what makes the difference.