If your mother has had this discussion with her surgery and they both agree that this is the best thing, there may be no reason for you to try to talk her out of it. If you’re concerned about the surgery, you could try to convince your mother to go for a second opinion to A) see if the surgery would help and B) if the second surgeon would do the same type of surgery or maybe suggest another one.
As frightening as surgery can be, studies have proven that people with certain types of back pain do recover well and have a significantly improved quality of life after the surgery.