cancer is not as deadly as it used to be.  as you said she is 19, so still young and i admagine she is in fairly good health.  That is good as it will help her with the treatments, and hopefully they found it early before it spread.  For what you should do, i think you should call her now, but dont stop there, here in canada we have a 24 hr relay to raise money for cancer research.  If you have something along those lines where abouts you are you should get your friends together and help raise money for cancer.  THat will show her you care, and it will help boost her spirit when it is low.  i wish your friend the best of luck, and remember there is alot you can do.