I think that your sister will definitely need a PEG tube.
Learning to swallow after a total Glossectomy requires the help of a Speech/swallow therapist plus plenty of practice.
Going through radiation is going to make this very difficult for her. She should still be able to swallow but I don't think she will be able to take in enough calories. Remember that many people who do still have a tongue need a PEG to maintain their caloric intake.
My Kris still has his PEG 21 months post his total Glossectomy even though he has not used it for 18 months.
I would be challenging the Dr on this. Yes, the Naso Gastric tube should come out, but I think only when they have placed a PEG. I don't think your sister will get through this without one.
Thank goodness she has you in her corner.
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!