First check for signs of dehydration.
Symptoms
Dry or sticky mouth
Low or no urine output; concentrated urine appears dark yellow
Not producing tears
Sunken eyes
Markedly sunken fontanelles (the soft spot on the top of the head) in an infant
Lethargic or comatose (with severe dehydration)
In addition to the symptoms of actual dehydration, you may also have vomiting, diarrhea, or the feeling that you "can't keep anything down", all of which could be causing
Things that are good to eat / drink are flat sodas (sprite etc) rice water (boil the rice and she can drink the water) , plain rice, plain crackers.
Start with sips of liquid, not too much.
If she's dehydrated and still can't keep anything down go the the ER, she'll need an IV. If she's not dehydrated and not keeping things down you might could call your DR for a Suppository anti-nausea medication.
Kids dehydrate quickly, especially if they aren't keeping anything down it is cause for concern.