This cancer can be very aggressive - my advice is to get her somewhere where she can have the surgery she needs - which sounds like a mandiblectomy and likely reconstruction of the affected areas - then possibly a follow up with chemo. There is always the option for a second opinion. She is very young to just give up! Plus if it hasn't hit her lungs or vital organs then it seems crazy to stop the fight.

I with is could suggest more but it seems like she really needs the surgery. Has she had a neck dissection? Best of luck with your mom... My prayers to you and your family.