J, Welcome, though I'm sorry to have to meet you this way. I'm so sorry about your daughter. My daughter, who will be 15 in November was diagnosed with TN when she was 11 years old. It completely sucks, and turned out world upside down. I will say, my daughter has now been medication free and mostly pain free since January 2014, so there is hope. No cure, but things that can really help depending on your situation.
I sent you a friend request, and am the one who runs, along with 3 other TN Mamas, a Facebook page for parents of kids with TN. I will happily add you into the group, but have to find you on Facebook first, so need to PM with real names and all.
My daughter was diagnosed, and then started on Trileptal (Oxcarbazepine), which is a derivative of Carbemazepine, which worked well for her initially. When it started to be unable to keep up with the pain, Gabapentin (Neurontin) was added in. As it was explained to me, Oxcarbazepine/Carbemazepine work to suppress neurological activity which prevents the nerves from triggering the pain response (and also causes the not-fun side effects of brain fog & forgetting things). The Neurontin works to shut down the pain response if it is triggered. So they can be safely combined and for some people the combined effect can really help. It did help our girl.
As for the scans, our daughter had a total of 3 MRIs taken. When we had the first scan done, we took it to a neurosurgeon, and he looked at it and told us it wasn't the right scan. :-/ Sooo, we went back and got the specific scan he needed to see the Trigeminal Nerve. We were told it was "Clear" and "Normal" by three neurosurgeons. We had another MRI done a year later, and it was also read as "Clear". However, long story short, we wound up having exploratory brain surgery done - I know, I hope that didn't completely freak you out, but there's a lot of back story there. In the end, 8 compressions of her Trigeminal Nerve were removed, her Trigeminal Nerve had grafted onto a membrane in her brain "like superglue" and that was detached. And 2 compressions were removed from her 7th cranial nerve and 2 more compressions from her 9th cranial nerve. Whew!
Moral of that story - NONE of that showed on her MRIs according to 4 different (over a period of years) neurosurgeons. Two of those at Johns Hopkins hospital (big deal hospital with a TN clinic). The final neurosurgeon (in California, we live in Virginia) we went to did see two of the compressions on the exact same MRI everyone else said was "clear", but there was still MUCH more going on that didn't show up.
I am happy to talk any time, and once we PM will add you to the Facebook group. All my best to you and your girl. I know it is incredibly hard and stressful. We missed a ton of school too. Just an encouragement that at this age, she can deal with her health issues first and catch up in school later. It's not fun, but doable.