Ignore the numbers. I know lots of stage IV colon cancer patients doing well many years later. I'm stage IV, and was also told 2 years, max 5 years, by one dr. I'm past 5 years now, and doing great; most likely cancer-free. Cancer was all over my omentum, encompassed my ovary, and was on the outside of my colon in several places (triple resection.) No lymph nodes affected.
Your mom might want to consult another dr - if she can get to a cancer specialty center, that might be the best.