Thank you for the query.
Such symptoms can appear due to acute gastroenterocolitis. In most cases this condition is caused by viral infection. Diarrhea
appears with fever and shivers. This should go away in a few days and should also leave temporal immune resistance for another viral infection. So another same episode is not characteristic for gastroenterocolitis.
Such symptoms can be also a result of some bacterial infection, allergy
or partial bowels obstruction. If your sister has fever as well, this indicates infection. If the symptoms do appear right after a meal, allergy is more possible. If she is over 50, have had constipations before or constipations and diarrheas alternately, this can be bowel obstruction.
I suggest your sister to
- If infection is most probable - start with liquid only diet until acute symptoms wont go away. She should also try Rifaximine and Nifuroxazide
(prescribed by her doctor) treatment with probiotics
- If allergy sounds most probable - elimination diet
- If obstruction is most probable - abdominal X-ray
and get scheduled for colonoscopy
Hope this will help.