You have not mentioned whether she fell from a height or while she was walking.
When a child has fall from a height there are a few danger signs one has to monitor :
1) abnormal behaviour
2) multiple vomits
3) bleed from ear and nose
Since your child has started vomiting
multiple times she is getting dehydrated and hence drowsy.if the impact of the head injury
was not from a height or forceful there are chances that these vomits could be due to viral gastritis
However I would suggest that you get her examined by her doctor to rule out possibility of head injury.