Arvind,
Just a few answers,

1. Yes, there has been a few here with NG tubes. PEG's seem to be the feeding tube of choice in general however and you can use a greater variety of foods as well. I can't speak for hygiene, cleanliness and water quality in foreign countries but relatively few in the US have problems with their PEG tubes. It seems to be more of a cultural thing - some foreign doctors don't use the PEG tubes and in the US they are practically mandated at many treatment centers.
2. Speech problems are common when nearing the end of treatment, trismus can also play a role. Many of us lost our ability to speak altogether for a while post Tx (usually only a few weeks). Mouth sores can play a big role in this and that is a result of not only RT but ct as well.
3. RT is monitored though CT scans adminstered at 3 week intervals typically. They might do a post Tx PET scan as well but remember early ones can have high false positive rates due to scaring. The "gold standard" is still direct visualization with mirrors or a scope and palpation.

And one last thing, "intolerable pain" is not acceptable. She has a basic right to adequate pain management. I would be her advocate and challenge the doctors for more powerful pain meds and a numbing mouth rinse as well.