So sorry to hear your Mom is going through all of this! I don't unfortunately have much advice other than what I've learned from being on this site, which is to try to get your mom's care from a cancer center. I attached the link below to see where there may be one in your area. Or, possibly, you may want to get a second opinion from a cancer center to see if they concur with what you have been told as far as treatment for this.

https://www.cancer.gov/research/nci-role/cancer-centers/find

Laura Age 40
Tongue lesion on left side grew and was hurting in mid-August
Dx as squamous cell carcinoma on 9.18.18
Left Neck Dissection and tongue surgery, lost a fourth of my tongue on 10.1.18, tumor had grown to a T3
Margins were clear except front section of tongue margin had three stray cancer cells that were not in the tumor
Additional surgery 10.18.18 to remove another cm near where the stray cells were found
33 radiation treatments from Nov 2018 through Jan 2019