I have absence epilepsy with seizures that are entirely subclinical. I can't drive until they are controlled and the medicine isn't working. They want me to try VNS, but its not proven to work for that. Let me know if you find out that it works.
I am very happy to hear that your daughter has done well with the VNS. The good response she has had thus far is encouraging, and there may be continued improvement over the next 12-18 months. There is no reason not to suspect that the VNS is also helping with the sub-clinical seizures, but without EEG monitoring there is no way to be sure.
The cognition issue is difficult. Frequent seizures or the anti-epileptics could contribute to poor cognition. Hopefully with the weaning of Tegretol the cognition will improve. Otherwise, ask your doctor at the Cleveland Clinic, and I am sure they could come up with a plan.
Good Luck