Hello! Thank you for the query. Such symptoms can be caused by several issues including food poisoning (bacterial or viral infection of the gastrointestinal tract), anxiety attack, inflammatory bowels disease, partial bowels obstruction. If dizziness is also without abdominal pain, heart issues, blood pressure drop should be also considered. I suggest your sister to visit a doctor. She should have some basic tests at the beginning like abdominal ultrasound, blood work, urine analysis, abdominal X-ray, stool tests, heart ECG. Hope this will help. Regards.