The colonoscopy is to follow up and make sure the bowel has healed. They are not looking for another problem, but to make sure that there is no additional perforation, infection, etc..... That is most likely.
Of course, to do a colonoscopy also rules out other possible problems, and gives her a clean slate; so for example, if she had diverticulosis, polyp, etc. they would spot these.
One of the issues might be: why the perforation.....
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