Stage of bowl cancer unknown

At the age of 87 my mother was diagnosed with bowel cancer. The professionals decided that, at her age and having COPD an operation was I’ll advised, and was given weeks/months rather than years.

One year later, several stones lighter, and an increased level of tiredness, we have no idea of what stage she may be. How does one establish whether it has spread and what stage it is.

The situation is very upsetting and stressful for her and the family.