Please, can anyone help me?

I have a dear friend whose sister (only 35 yrs old) is dying of colon cancer. It is in Stage 4. She has medical insurance, but they won't pay for the treatment/surgery and subsequently, the doctors won't provide treatment without guaranteed payment. Time is short, but saving her is not out of the question. It all comes down to money. Insurance companies never like to pay, but a lawsuit would take too long. Does anyone have ANY advice on what to do from here or who she can call about this?