My daughter of 2 years had 3 days vomiting she was prescribed ondansetron she took it for 2 days but today she didn't take it and vomited. ?

Have her rechecked.: It's best in this situation to have her rechecked to make sure she hasn't developed a new problem (like an ear infection) since she was last seen.

Not to worry: Recurrent vomiting several times after meds stopped is not at all unusual vomiting with GI viruses can continue it seems forever in some children however if vomiting continues esp if severe recheck is always a good idea.