Me, my 7-year-old, and my 5-year-old have all had two colonoscopies apiece. It's an easy procedure, and she almost certainly doesn't have cancer.
On the other hand, she almost certainly does have
something. Maybe Celiac, maybe Crohn's, maybe the ubiquitous "we can't figure out what else it is so let's just call it" IBD...
Anyway, all the regular dwellars know my family's saga with digestive disease, and how I'm a huge proponent of treating with diet. (I'm not against prescriptions, but I see them as a stopgap measure while you work your way into remission.) Feel free to PM me after your sister gets a diagnosis if you want to hear me yammer about it some more.