Have her do the Chemo.
My brother (an extremely healthy 43 year old) was diagnosed with Renal Cell a couple years back and had his Kidney removed. They said they believed they got it all and had no need for additional medications. He recently broke his Femur and was then diagnosed with Secondary Bone in the Femur, this has since spread to his jaw; his rib; his skull; and his lymph node. His has undergone major surgery in his arm/radiation. Then went through radiation for his jaw. This ugly monster got loose and now is running crazy throughout his body.
The follow up medication for your mom would probably keep any "cells" that may have traveled through her system under control. Just stand by her; love her through it all and keep the faith.
No matter what I have written above, we still have Faith this will work out for my brother, and that is a big part of the battle.
God Bless you and your family.