If the same strains are prevalent down there, the snap test should be able to narrow it down to Lyme's, Anaplasma or Ehrlichia exposure. Regardless, I think I'd ask for an extra week of doxy if it's anaplasmosis or ehrlichiosis.
Are you giving her a probiotic at some point during the day (best would be a few hours before or after giving her the antibiotic)? Doxy can be really hard on the gut and we've found that daily probiotic helps a lot. We just use an inexpensive acidopholus for human use that comes in capsule form--if you want to, you can just open the capsule and sprinkle it over food.
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