I'm sorry. My mom was treated for breast cancer in 2006 (had a double mastectomy and chemo) and it hasn't come back. The chemo and following medications did a number on her and she's never been the same healthwise, but she's ok and enjoying a full, active life. I hope the same for your mom.
I'm so sorry, I can only imagine how scary this must be for you and your family. I hope that catching it and addressing it so early will help with the good prognosis she was given.