Maybe you could send your friend a card, there are some really expressive ones, sometimes a bit difficult to choose, you can get quite choked reading them in a shop.
My sister in law was diagnosed with breast cancer 18m ago, she is 34 and had her right breast removed two weeks after diagnosis. She had a VERY positive frame of mind, everyone fell apart around her but she insisted on everybody being strong, she shamed us all!
We did a box for her with all little bits & pieces, some books written by survivors of breast cancer (from Amazon.co.uk), angel pins (from card shop), crystals for health & love (again from card or gift shop) and I wrote a poem as I couldnt express myself to her without being upset. She said she loved it and whenever she felt a bit down or sad, she looked through her box of goodies, she said the books were a great help too.
She has just recently had reconstructive surgery and is really pleased with her new boob, she has a way to go but she's on the right track. She faced it head on and as she has 4 children, she wasnt gonna let it beat her.
Just letting your friend know you are there for her will be a massive boost, she is prob in despair and will need a lot of help, just be there for her. Thinking of you both x