A. if these symptoms all came together it's very likely to be a severe food allergy. Blood in the stools should always be considered a serious matter as some severe gastrointestinal infections could be life threatening if left untreated. A strict hypoallergenic diet will probably be the most important part of the treatment on the long run but right now she probably need more than this (meds to stop the allergy, anti emetic to stop vomiting, antibiotics to treat possible gastrointestinal infection). I advice taking her to the vet ASAP.
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