I find it tiring when people decide it's their job to manage other people's healthcare. My best friend's mom had colon cancer last year (caught early and she's fine now), and the whole family became very active in promoting colon cancer awareness. I really appreciated that my friend did not project her fears onto me, and did not even suggest that I get a colonoscopy because she trusts me to make my own decisions about my own health.
As I understand it, your friend is of an age where colonoscopy's are generally recommended so it was ok to mention it to her, although I'd think her doctor would be recommending it as well if they think it's necessary.
One other thing to consider is that there is some controversy over the effectiveness of mammograms, and I'm sure a lot of people feel very strongly about it on both sides. Because of this, I would never presume that it's appropriate to push someone to get one.