What should a sick person be doing to get better as soon as possible?

my friend is really sick and she doesn't know why.. she has been throwing up everything she has eaten even chicken broth and saltines. and she feels like poop and she doesn't know why! also she has little red bumps on her body and they look like chicken pocs but shes not itchy at all what should she be doing to get better? preferably as soon as possible because school starts tomorrow and i don't think it would be a good idea for her to miss the first day of school but if shes still sick i don't want her to go.