Having very bizarre diarrhea issues with my 1.5 year old

She's been having diarrhea for a month. The cycle keeps repeating itself - I put her on chicken and rice, she doesn't poop for 2 days, then she poops fine. Then I put her on dog food mixed with the chicken rice and she has diarrhea immediately. I thought maybe she was allergic to dog food but I put her on organic dog food where chicken is number one ingredient. I don't know what else to try?

Should I put her on chicken and rice forever and then maybe blend in some cheese and other healthy fats? Is it possible she has a virus or a bug in this scenario? her behavior and energy is perfect and like I said, she doesn't poop for 1-2 days when I put her on rice and chicken. Surely she would keep having diarrhea if there was a bug?

I had a vet examine her and they said she's fine.