So recently a close friend of mine was told she may have cancer and I really don't know what to do I'm trying to be upbeat but you can tell its weighing on her
Just be there for her. Help her get through this. Make her smile an laugh when possible. That's all you can do and that's all anyone can ever ask of any close friend.
I agree with the idea of just being there for her. And try to spend as many happy and laughable moments as possible When I was in highschool one of my closest friends had cancer, and because of some stupid sh*t that happened some time before I stopped spending a lot of time with her. She died later and I truly regretted it, but I remembered all my efforts and talks with her when she had cancer, and I stopped blaming myself. She had a hard time but still lived a full-fledged life in that time. I believe there will always be hard times in these cases, but they get overshadowed if a good amount of happiness is in the mix.