Hello,
Thanks for using HCM.
I have gone through your query and I can understand your concerns.
As per your description,I suspect a possibility of 
gastroenteritis. It is quite common in children and it is sometimes called "stomach flu".
You don't need to worry too much because it can be cured with timely treatment and complications are very rare.
I suggest you to 
consult a pediatrician and get the following things done:-
1.Since she is fatigued,fluid replacement is required which is by oral route or rarely by intravenous depending on the severity of the illness.
2.Appropriate antibiotic therapy may be needed to tackle the infection.
3.Supportive management like 
acetaminophen for fever and antiemetics for vomiting can be given.
4.Basic blood investigation and stool routine examination may be needed.
If the symptoms persist despite all these additional investigations and evaluation may be required which might include an 
ultrasound abdomen.
You can prevent gastroenteritis and food 
poisoning by practicing the following measures. 
1.Teach proper hand washing  before and after having food.
2.Trim the nails short.
3.Keep raw foods separate from ready-to-eat foods.
4.Cook food thoroughly.
Hope I have answered your query.
Wishing you good health.
Regards.
Dr.Shinas