Hi SoloMomma,
If she's not running a fever, she could have a simple stomach virus (some don't elevate temperature much or at all), or she could have eaten something that's given her a round of food poisoning. It's good that the vomiting has stopped, but you need to try to rehydrate her. I'm a little concerned about the lethargy. It could just be an effect of the dehydration, but it could also be an indication of encephalitis or meningitis. Try to wake her up and see if you can get her to a full state of wakefulness, even if it means she's crying. Check to make sure that she doesn't have a stiff neck, and also watch for a petichial rash (small red/purple rash, usually on the arms or legs, but could also appear at the base of the neck along the spine. If you see any of these signs, head to the ER immediately.
If she can be roused but still won't urinate, you need to get her rehydrated. Do NOT give her straight water. She needs an electrolyte solution to restore proper chemical balance. Chicken broth is better, but it still doesn't contain the right composition of electrolytes that need to be replaced. If she won't take the pedialyte you can try the World Health Organization (WHO) oral rehydration solution:
1/2 tsp table salt (NaCl)
1/2 tsp salt substitute (KCl)
1/2 tsp baking soda (NaHCO3)
2 Tbsp sugar
1 liter chilled water.
Morton's makes a salt substitute that's 50% NaCl and 50% KCl. If you get this, use 1 tsp of it instead of the 1/2 tsp each of table salt and salt substitute.
Try to get her to take 1 - 2 Tbsp of this every 10 - 15 minutes. I had a pretty bad bout of gastroenteritis last week and lost over 1 lb of fluid in about 12 hours. I have to say, this solution tasted pretty good and I managed to get 1.5 liters of it down in a couple of hours.
If you can't get any fluids in her by the morning and she's still not urinating, you must take her to the ER for IV rehydration. Also, watch for a fever over 101.3, rapid respiration, or rapid pulse. These can be signs of a more serious infection and onset of sepsis.
Now that I've given you the worst case scenarios, you should know that this is probably just a mild bug and your daughter will be just fine once she feels up to drinking again.