I just want to assure you that healthy diet is best defense for the body. Maintaining Proper Oral Hygiene is a first priority to prevent flu. If you decided to have her take a vaccine, I highly suggest that she take it any time between 8 am and 12 pm and be monitored for the next 24,48,72 hours for any over reaction.  A full medical check up is mandatory. Vaccines are helpful to prevent many diseases nut little percussion ( diet, not to drive, warm fluids) can help to prevent fever.  If you notice any sever rush or sever dizziness reported immediately to your family doctor. I had many vaccines when I was at school in the 80s. Indeed vaccines are not just like drinking water. But it will benefits your child if you take all percussion . The clinic should provide with full pre- and post- operative (giving the injection)  instructions to get your child ready to take the vaccine. Read ampule details carefully. Place of manufacture.