Janie

Actually most base of tongue cancers that are advanced ( or "very bad")are NOT treated by surgery at first, especially stage IV but by radiation and chemotherapy since the doctors are being candid about what a rough road surgery puts you on. (Tumors on other parts of the tongue are a different story and most do get surgery right off the bat). So she may not need the surgery.
Look at DavidCPA's signature line and you will see that for many base of tongue cancer patients, radiation & chemo do the trick. Or look at Mike Douglas' experience. With just a scope examination and no CT , MRI or Petscan yet, it is possible the doctors will reconsider surgery.

The more difficult question is about motivating her. If the primary reason she wants to give up is because she can't drink anymore, then she could always get a feeding tube and put wine down the feeding tube. Since the alcohol never touches any part of the mouth or oral cavity, most doctors think it's fine. I make no apologies for liking a drink and found my beer a day the first time around and my wine in the feeding tube since my surgery very nice. My doctors have all signed off on it. However, since she was a functional alcoholic, she probably will not admit that fear of not drinking and facing life sober is the reason. If she can not or will not drink sensibly and in moderation, it certainly would be better for her to quit entirely.
You sound like a great sister. Welcome to OCF
Charm