I am so sorry to hear this. This really hits home for me, as Saturday will be the 1 year mark of the passing of my friend and co-worker from metastatic breast cancer. She was diagnosed at 37 and passed at 40. Her breast cancer moved to the lining of her lungs. It was devistating.
Talk with your friend. Ask if you can take her to lunch (somewhere private) or take a walk with you just to talk. Tell her you want to support her and that you want to know what she needs from her friends. My friend really wanted us to just spend time and help keep her busy and feeling normal. She did not want us to feel sorry for her to to dwell on her illness, she wanted to live a normal life as much as she could and get her mind off things and laugh. Ask her if she wants to keep this private, she might not want everyone at work to know b/c then she will feel like everyone is treating her different. If she is OK with others knowing, rally the troops. When my friend was doing chemo we would bring care packages to her house. Magazines, gatorade type drinks (she said chemo made her very thirsty), puzzles, cards, anything we could think of to brighten her day. We helped take care of her dog when she was not feeling well. We wrote notes of support randomly and sent them to her all the time. When she passed, we all found all the pictures we had of her (some of us worked together 10+ years and were close outside work as well) and put together a photo album of her life at work and gave it to her family.
With all my heart, I hope your friends situation turns out differently than mine. There is ALWAYS hope; please help her find hope in her heart. Hugs to you both.