So sorry you are facing this stomach virus! While stomach viruses are generally short lived we do see some that last the better part of a week. Treatment depends on the severity of symptoms, the age of the child and the degree of dehydration. My advice is that if you don’t like the way things are going, head back to the doctor. They can check for dehydration and can discuss with you treatment options. It never hurts to have eyes and hands on a little one when they are ill, especially if you were already there but things are NOT getting better. At best, they can help. At worst, they can make you feel better that there is nothing more serious going on.
As for the flu shot helping with stomach viruses, that is unlikely. The flu shot protects against influenza which is a different virus from those that cause the typical stomach bug. Nevertheless, the CDC recommends annual flu vaccination for all children aged 6 months and over. If your daughter is over the age of 2, she can receive the nasal mist flu “shot” which is wonderful and not painful.