Hi Swati, I also happen to be a caregiver to my father who has just completed treatment for his recurrence. He had his treatment here in RGCI, New Delhi.
With doctors, you have to be very clear as to what you are asking to convince them. Since your mother had a recurrence in tongue, total glossectomy seems to be the only choice that doctors have. Doctors may not be looking for CT scan as they are not suspecting any mets to nodes (since the new one is small). Once the surgery is over, probably they will look at re-radiation with chemo.
And, I would suggest that you visit your mother as being there it puts you in more difficult situation. Whatever the stats says, early recurrence are also curable. Only doctors have to put more efforts to work out a feasible treatment plan.
All the best, we all are there to help.