One of my best friends cousins was diagnosed with a brain tumor, another friends sister also had a brain tumor, and I used to babysit for 7 hours a day for a 2-year-old girl with leukemia - so I know all about cancer.
All I can say is it's very emotionally straining for them, and possibly even moreso for their family and friends. It's awful when it happens to someone you know, but think positive - they will get through it, they will be okay - and maybe it will turn out for the best. Sometimes it does. Sometimes the good guys get some luck. And what doesn't kill you makes you stronger, afterall. Imagine what an independent person your friend will be when she gets better.
As for survival stories, both of the people I've known with brain tumors fought them and lived. One went through Chemo (sp?) and killed it, and another had surgery, but is living however a normal life she can. The little girl still has five more years of chemo to go before we'll know anything, but our fingers are crossed. I'm sure everything will turn out for the best.
My heart goes out to you and your friend. Good luck. And tell her get well soon from me.
<33 Jess