Help,

My mum has been told by her doctor that they believe she has Bowel Cancer. She has had blood pressure issues for a couple of years and has been on mediation. A few weeks ago, she went for a blood pressure check and was told it was dangerously high. They changed her tablets and thought it would sort it out. It didn't and they ran some more blood tests and told her she was Anemic with servire iron deficiency. That was on Friday the 5th May and she was referred for an urgent CT scan. She had the scan on Tuesday 9th May and a few days later the GP rang and said 90% sure it was Bowel cancer. 

Now she has a colonoscopy booked for this Thursday afternoon. She seems to be dealing with it OK but I'm panicking (not in front of her). 

Is it normal to have a CT scan before a colonoscopy? Does this mean they've definatly seen cancer and are now going to biopsy or could it still be something else such as a polyp?