If your friend is around your age (15), I doubt every seriously that she was diagnosed with colon cancer; no matter what she says she has, or what she thinks she had one year ago. She's too young to develop colon cancer.
She was probably diagnosed with colon polyps, and misunderstood the diagnosis; or else she's putting you on. Polyps aren't usually cancerous, and they can be removed though an endoscopy or an colonoscopy.
If she had been diagnosed with colon cancer one year ago, she would have undergone major colon surgery very soon afterward, and she might still be receiving chemo as a follow-up.
If she tells you again that she was diagnosed with colon cancer one year ago, ask her to show you her surgical scar.