Hi, momof3girls.
I'm sorry your mother is in pain, but that she's been diagnosed is at least a step in the right direction! I have glossopharyngeal neuralgia (same thing, different nerve) and I take Neurontin for it.
200 mg/day is a *very* low dose. If your mother is older and pretty light weight, this may be part of the reason the neurologist started off slowly. I'm an otherwise healthy 23 y.o. and I currently take 900 mg of neurontin a day (300 mg per pill, 3 times daily). I know there are people who take 1800 mg of neurontin a day or more (like Nik-key, here), and I'm actually hoping to get my dosage increased to 1200 mg/day soon.
I would definitely talk to the doctor about having the dosage increased, especially since you are seeing some beneficial effects. Neurontin typically carries fewer risks and side effects than Tegretol, so people often start out on that. It is important, though, that dosage not be increased or decreased too rapidly, and the neurologist will know what is safe.
I am in Nashville, too, if I can do anything to help. Also, I know that the department of radiation oncology at Vanderbilt has treated TN before using stereotactic radiosurgery, which is similar to gammaknife, if you're interested in that. It provides an option to those who are unable to undergo surgery.
Keep us updated, and good luck!