Mom Had HER 2 Positive Breast Cancer 2 Yrs. Ago.

Mom had HER 2 positive breast cancer 2 yrs. ago. Took 12 chemo treatments & 21 radiation treatments & had lumpectomy. When she was done with chemo she took Herceptin every 3 weeks. Was just about done with radiation when she found another lump. This time it was one with a different protein that chemo or radiation wouldn't work on. It ended up being a very small tumor on her lymph node. We all decide as a family for her to have a right-sided mastectomy & she had 13 lymph nodes removed. The Surgeon said he got it all. She'll see Oncologist next week & is scared she will have to go through chemo again. I think maybe she'll just have to go on Herceptin as a preventative measure. She's also scared more tumor will come back to other places. Do you have any advice Doctor. Thank you.