Hi M.,
This could just be a tummy bug -- some can last a week or longer, and be relatively minor. I second Mommyc's advice though -- cut out all dairy for at least a week. If the vomitting continues, a trip to the doctor is in order. If not, after she has not vomitted for at least a week, give her one serving of milk or yogurt and nothing else, then see what happens. If she vomits shortly after eating, you should consider that she might have either a cow's milk allergy or a milk intolerance. If so, again, a trip to the doctor is in order for testing to get a true diagnosis. If you don't want to subject your toddler to prick testing, all three of the major blood tests available for allergy testing (Phadia, Siemens, and Hycor) have been shown to be just as sensitive and fairly equally specific, and can be ordered by your pediatrician.
While milk allergy is one of the most common allergies in children, in reality, no more than 9% of the population has a true milk allergy, but up to 25% of the population THINKS that they or their child has a milk allergy. Needless to say, a lot of people cut out dairy products unnecessarily, which, in some cases, can lead to a nutritional deficiency.
BTW, do either you or your husband have any allergies? If you don't, this lowers the likelihood that your daughter is atopic (that is, has a genetic predispostion to allergy). Conversely, if either you or your husband has any kind of allergy, this increases the possibility that your daughter may develop an allergy of some kind. Allergies can manifest at any time of life and usually require some degree of sensitization before symptoms appear, so something that was handled safely in the past could still cause allergic symptoms later.