Tamiflu's side effects are basically the same thing as the flu. Fever, nausea, joint pain. You have less side effects if you take it with food but of course with the flu the last thing you want to do is eat anything so you end up with the side effects.
DON'T TAKE HER BACK TO THE DOCTOR'S OFFICE!!!! At this point if you have any concerns just call the office. If they feel she needs to be seen again they'll let you know. At this time of year the physician's offices are what I term as 'germfests' because everyone seems to be sick this time of year. You don't want her to pick up something else on top of the flu or get a different strain of flu. Keep her home and resting unless she gets worse.