There are several reasons why this can happen:
Does she have a fever?
Either way,if a child is sick then a lot of times they won't eat and when you try to feed them it will come back up. As long as she isn't dehydrated you could just give her some time and sips of pedialyte. Sips only though, and only every so often.
Some ways to tell if they are dehydrated are dry cracking lips, crying without tears, doughy texture to the skin.
You did the right thing in calling the pediatrician. But they will probably just tell you to watch her for the next 24 hours.
Make sure you don't give her anything to eat unless she acts hungry and even then only bland foods like white rice, mashed potatoes, crackers, etc. And only in very small amounts then work her back up to normal food as she tolerates it.
HOWEVER!!! If she has projectile vomiting or could have fallen and hit her head or her stomach she needs to be seen right away.
Hope this helped, let me know how she is doing if you don't mind.
I'll be praying in the mean time....