Hello Martin and thanks for your query
Your daughter needs a urgent treatment for blood motions. These are due to infection in the colon
or intestine or may be due to liver
disorders. Needs to be investigated in detail. She needs a course of antibiotics, plenty of fluid to over come dehydration
and electrolyte powder in water. You can give milk and ORS
, these will over come dehydration and electrolyte imbalance
Make sure that she will pass urine at regular interval but not passing urine than it might effect Kidneys.
Consult your doctor get some investigation done and get to a diagnosis and cause for bleeding.
Till that give fluid and semiliquid diet.
Best Wishes and get well soon