Try to stay as positive as you can..........she needs you to be strong for her.  Easier said than done I know, but remember, she is probably worried sick right now and she needs your strength so that she can hold herself together.  Also, what you have described is NOT necessarily cancer..........it could be many things.  We  all jump to the conclusion that it is cancer when we have got some health issue, but the truth is, there are lots of illnesses that mimic the signs of cancer, and like I have already said, it could literally be anything.  When you are with her, put on a brave smile and tell her that everything is going to be just fine.  Good luck.