Brief Answer:
Most likely irritable bowel syndrome.

Detailed Answer:
Hi

Thank you for asking HCM

I have gone through your query. Your wife's problem can be most likely irritable bowel syndrome. It is just a functional disorder and mostly stimulated by stress or anxiety.
Avoid antibiotics. You can give probiotics like bifidobacter or sacharomycces boulardii. Give fluids and electrolytes according to lose. Taking banana , yogurt is good.
Get a stool routine to rule out any infections.
You can give loperamide to arrest the diarrhea. Taking pepper mint oil will be soothing. Taking antispasmodics like dicyclomine will be helpful to relieve the pain also.
Drugs like antidepressants are helpful in this. But before that talk therapy with psychologist should be tried. A consultation with Gastroenterologist is well appreciated.

Let me know if anything not clear.
I am happy to help you.
Thanks.

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