I'm so sorry Steph, I know that must have been a terrible shock for you
My mom died of cancer about four years ago (not breast...pancreatic) and I was with her through all her treatments and everything so if you ever need anyone to talk to, feel free to email me and I'll try and help any way I can.
That being said, try and keep your spirits up, because as many other people have already said, they've come a long way in treating breast cancer. My great-Aunt has had it 3 times now and is still doing well. She beat it twice and it just came back this winter. She's 86 so she figured this was probably it but she's actually gone into remission again! So you never know. She also has the most positive outlook on life of anyone I know, so I guess there really is something to be said for positive thinking