Please help my mother recover from breast cancer final stage

My mom has had a large lump on her breast that just kept growing and growing. We didn't think it was cancer.. Who would? We thought it was a cyst of some sort. She went to get it tested after prolonging it for personal reasons and it got worse and worse. We got the call that it indeed was cancer. She broke down to me. I'm her person and she is my person. We are trying to cope with this. It has attacked her lymph nodes already and is advanced they said.  I am 19 years old, studying... She's 45. She is way to young. i constantly have thoughts of losing her and how i am not strong enough but i have to be strong for her. I guess my question is how can i help her, because she is sure as hell scared. So am I. I don't know how to cope..my father left us the day I born and my grand parents are taking care of us.