Something similar happend to me about 15 years ago after many courses of Antibiotics
over a year's period. Has your sister been on a lot of Antibiotics
lately? If that's the case, you should research Candida overgrowth on the net and Leaky Gut Syndrome--there are also forums for both her on curezone. People with leaky gut get itchy because there are holes in their intestines caused by Candida overgrowth/pathogenic bacteria. The vomiting is perplexing but could be that there is candida or other unfavorable bacteria growing in her stomach as well. If she were my sister, I would help her find a doc that is knowledgeable in parasitic infections, including candida, and who will do a stool/saliva culture to figure out what is going on in her intestinal tract.