The problem with most chemo is that it destroys the immune system. So, you do not die of cancer but of something else. You often do not live longer, some die directly of their first chemo session but the doctors do not want to tell you about that. I knew a lady who had about a year to a year and a half to live with basically the same thing, endometrial cancer. She decided on chemo, took one session, which devastated her and she was gone in less than 4 months.
The worst part of chemo is that you spend what is left of your life in misery. These poisons do not make you feel better which is what some alternatives do.
The choice is up to your mom but she should remember that the oncologist makes a LOT of money off of the chemo, so the oncologist is going to encourage it, possibly even where it may not have much benefit and possibly where it may actually be detrimental.
What it comes down to is not necessarily how long you want to live, but how you want to live.
I always recommend that before making a decision that the person with cancer read Dr. Hulda Clark 's book the "Cure for All Cancer". While she was not perfect, there are many people alive today, that had been sent home to die, due to her therapies. You do not have to go to a clinic or a doctor for this.