Gee she is very lucky to have you for a friend. But, I afraid there is nothing I know you can do. Does she have any family around that knows what is going on? First of all most people don't want to hear someone else complain, but to top it off someone not willing to do anything for themselves is even more incredible. I am not sure I could do want you are by listening to her moan and groan and not be willing to a thing to help herself. This is going to get old after awhile I am afraid. Something else you may need to watch for is how she is affecting you. If she gets you all uptight and stressed this will only aggravate your own problems, so be aware of that. Some people can just suck the life out of others.
Even if you let the nurse at the drs office know what is going on with her, they cannot force her to come in. Since she has this fear of everything being cancer, she may be in need of some counseling. Have you spoken with the minister at your church about this lady? Its a long shot, but it may be worth a shot.
I wish I could tell you something more positive but, you are really in a no win situation with this person. No one can force her to do anything. She may have all these fears you have spoken of, but in reality if a person is in severe pain they are going to go to the dr no matter what, cancer fear whatever, you would want some one to check you out and see what is going on.
It may be best that you step aside and not be so available to her for a bit of time. If you are her sounding board give yourself a break because you are obviously very worried about her. I would really hate to see this mess cause you extra problems because its enough as it is w/o someone else adding to the mix. Hugs to you. Susie