I do feel that you should be talking to your Mother about this diagnosis.
She is obviously aware of the diagnosis and I am sure that she would want to discuss this with her family. She will need to know that you will be there for her , advocating and supporting her. You do need to talk to her to find out what she wants. This is the most important thing. What, She, wants.
Once a treatment plan is offered, you will need to talk about this with her. What is involved. How she might experience this. What side effects there may be. What is the likely outcome and what the longer term consequences may be. What her quality of life will be. You really need to discuss these things and what she really wants to do, given her age. Make sure that she really does understand all this. Does she want treatment or is she going along with what her family want or expect. To me, it is paramount that you do understand exactly what your Mother wants.
Not easy.
Tammy

Caregiver/advocate to Husband Kris age 59@ diagnosis
DX Dec '10 SCC BOT T4aN2bM0 HPV+ve.Cisplatin x3 35 IMRT.
PET 6/11 clear.
R) level 2-4 neck dissection 8/1/11 to remove residual node - necrotic with NED
Feb '12 Ca back.. 3/8/12 total glossectomy/laryngectomy/bilat neck dissection/partial pharyngectomy etc. clear margins. All nodes negative for disease. PEG in.
March 2017 - 5 years disease free. Woohoo!