Sounds like she threw up bile. I would say if everything seems fine, then it was probably just one of those "odd" things. But if it happens again, or if the stomach pain returns...you might advise her to get her gallbladder checked out. Vomiting bile (can be yellow colored or green) is sometimes not a cause for concern, as if her stomach was empty when she threw up....this would be the reason for bile to come up. Like I said, if all is fine now...no more issues, Id say she is ok....but if it starts happeneing on a normal occasion, might check it out to be safe.
Food poisoning? Is she pregnant? Kinda hard to tell but glad she is feeling better...