Abigail has had headaches, stomach cramps, and diarrhea for over 24 hours. Not much urine output. When should I worry and/or head to the hospital?

Needs hydration. Hydration in someone who is dehydrated can be intravenously or can be done orally if you can get enough liquids in. Water, half strength apple juice, but I like the traditional chicken noodle soup or agua de arroz because of the starches. If she is droopy and lethargic, then do not pass go - straight to the ER.
Hospital? Virginia259, If she has had diarrea for one week and is not putting out urine the time to go to the hospital is NOW thanks.
Reduced urine output. Reduced urine output in the setting of fluid loss could be dehydration or kidneys may shut down from the infection itself, in wither case patient needs iv fluids take her to hospital.