Sorry to hear about your friend Debbie.
I think the thing with this is why we find it hard to deal with is the fact that it could happen to any of us at any time, and its scary.
I think as long as you are there for your friend thats all you can do.
If it were me that was ill i would want my friends to treat me as normal and not make to much fuss about it and not be miserable for me, that would make me feel worse.
Just carry on being the good friend you are,
I wish your friend the very best for the future.