Having family and friends that have or have had cancer is a scary thing. The knowledge that all of us can have cancer is not a welcome realization. You cannot let fear paralyze you throughout your life. My suggestion to you is to research as much as you can about the cancers you know about. Also read literature from the American Cancer Society, Breast Cancer organizations etc. The more you know the more powerful you become and less fearful. It seems we always fear that which we do now understand. You are not alone as many of this boards memberhip will tell you.
It sounds like your Mother is doing well. Take comfort in that. I did not have any family history of breast cancer either. My daughter knows that she needs to be diligent in her breast care as I have survived cancer but she also knows that the type of breast cancer I had (there are 15 types of breast cancer) she will likely never develop.
Early detection of any type of illness is key. Be consistent in check-ups from a doctor you trust. If you do have a doctor that you trust and they know your history and mother's ask him/her about the cancer and what you need to do to protect yourself and be pro-active.
Talk with your Mother. She is your best advocate, other than you, that is. Try to be close to her and listen to what she can tell you about her physical and emotional being. It will help you to know and help her to talk about what she is going through.
If you are a spiritual person, pray and have discussions with the spirit within you. For me, the power of prayer, is the ultimate consolation and counsel.
Good luck and I will have you and your Mother in my prayers.
Two are better than one, because they have a good return for their work: if one falls down, his friend can help him up. Ecclesiastes 4:9-10