D.B.
Usually when the immune system is weakened, they are susceptible to new infections (viral or bacterial). But what also happens is they start to feel better, are so bored with sitting around, and jump back into full activities. They don't realize that healing is energy-consuming. So they really have to limit activities and go back slowly, and they have to sleep more - the naps are telling you that.
You don't need the ER. You may not even need the doctor at least after the initial diagnosis. A low grade fever is the sign that the body is working to fight the infection - not a reason to rush in to be seen. (Different if there's a possibility of strep or something bacterial that won't heal on its own.) In fact, it's not usually a good idea to medicate a fever unless it's above 101 or unless the kid is so uncomfortable (like aches from the flu). Just let it be - fluids, rest, sleep, repeat.
If she's not drinking water, find other options - popsicles, water-rich fruits like watermelon, soups, regular seltzer (plain or with flavor), etc.
But tell her that feeling "normal" doesn't mean she's done - limit the activities! She'll be ticked off but too bad. Her body is telling her she is run down. Get some movies, get out the board games, do a jigsaw puzzle - anything that's fun but which doesn't involve running around and which can be started/stopped when someone's tired.
