I don't have breast cancer, but I do have many other health problems. I don't believe that my illness is all there is to me, and when people push the ribbons and colors and what not I feel like they are saying that is the only thing about me that matters anymore. I know that's not what they mean, and many people with health problems don't feel that way, but I do. Some others just don't want yet another reminder.
For someone you don't know well, I would not do ribbons. Do you know what colors she likes? If she has historically worn a lot of pink or used it some in decorating or what not I think using pink would be fine, because she likes it. But I'm not sure using pink only because it's breast cancer's color is the greatest idea.
I would use colors you know she likes, because there are no risks of that being a painful reminder.