How can I support my daughter through a medical decision involving abortion?

My daughter is twenty nine years old and married to a wonderful young man. She learned that she was pregnant about a month ago,and she was ecstatic, as was I. Long story short, she has just been diagnosed with invasive breast cancer that will require surgery, chemotherapy, and possibly radiation. It has been strongly suggested that she abort this pregnancy to pursue treatment, because waiting could end her life. I know she desperately wants this baby, and I also truly want a grandchild, but I am terrified by the risk. I am devastated by everything and I do not know what to tell her, and I feel like a horrible mother. What should I do?