Oh poor thing. Will be tough on her own. Very shocking for you to think about.
But don't panic.
My SIL had mastectomy, chemo and radio nearly 5 years ago - very agressive treatment, as she was about the same age as your friend, and 2 young kids.
The chemo was challenging - but not as bad as she had feared. She had chemo every two weeks, felt all fluey and poorly for two-three days each time, but went to work the rest of the time (felt ok, and needed her life to remain as normal as poss to keep her mind occupied, I think).
Has she any family nearby, or who could come for when she is recovering from surgery?
There's lots you CAN do - you can get friends galvanised into a schedule of practical help, get people to call her, visit, send cards at well spaced intervals and keep her spirits up, I know my SILs best friend transformed the experience of losing her hair, by going with her to a wig fitting and making it hilarious. Take her good nourishing meals when she is feeling crap, to build her up.
Very hard news, but breast cancer is mostly considered treatable these days, Alexsmum.
Do you know what her consultant has said to her?