Hello dear,
Welcome to HCM. I hope that it is bug,but child usually can vomit in these cases:
1.
Fever (intoxication)
2.Poisoning
3.Overeating
4.Cyclic vomiting
5.Intestine infection
6.UTI
7.Worms in intestine and etc.
  I suggest-
-Avoid proteins and fatty food, give only carbohydrates(boiled potto, rice,vegetable soup)
-Avoid uric acid riched products(chocolate, peas, sour juices, market juices,spinach, beets,tomato)
-For absorbtion of toxins 
charcoal 1 tablet/10 kg/day is very useful, you can divide dosage during day
-
Econorm 1 packet 2 times 3 days
-For keeping hydrated your child you can use ORS ,  give to her to sip 5-10 ml every 5 minutes.
-For 
nausea,vomiting give please domperidon or 
ondansetron 1 tablet 2 times 
-If vomiting will repeat you should startantibioyic-ofloxacin10mg/kg/day
 Take care
  Recovery soon 
  Dr.Sagar Gaurav Shrivastva