I'm sorry to hear that! I know first hand how scary it is, Brian's cancer was the worst thing that ever happened! I encourage you to visit the web page for the American Cancer Society, they have tons of useful information that is easy to understand. www.acs.org If you ever want to talk to someone who has been there please pm me anytime!
My best advise is to be there for you mother. Cancer patients also need an advocate, they are understandable VERY scared and can forget to ask important questions, or forget important details about they're own care. You can help her remember. If you or her think of questions for the doctor write them down so you don't forget. I know its hard but you can be a big help to your mom now.