Demioyin,
Welcome to the Forum! I'm glad you found us here.
I'm sorry your daughter is struggling so. As if seizures aren't enough, the medication can make things doubly difficult.
I assume the doc added the phenobarbital because her seizures weren't under control with Tegretol alone?
Here's a NIH handout on Phenobarbital.
http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0000542#a682007-sideEffects
Also one on Tegretol:
http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0000620#a682237-sideEffects
Phenobarbital can cause excitement, especially in children. She's a young adult now, but the same side effect can apply. Tegretol can cause anxiety, confusion and memory problems, loss of touch with reality, among other things.
Has she been tested by a neuro-psychologist? I'm wondering if the developmental delays that you suspect are actually thinking and memory problems caused by the Tegretol. Another drug, Trileptal, made incredibly mentally slow. I had trouble understanding and answering people, I made huge mistakes many times a day, and was deeply depressed. I pretty much had pudding for a brain. If someone had first met me while I was on that stuff, they would have thought I was developmentally delayed, too.
Epilepsy and developmental delays can be comorbid (happen together). In some cases they've found the cause:
Genetic Defect Found to Cause Severe Epilepsy and Mental Retardation
http://www.sciencedaily.com/releases/2010/10/101012151232.htm
It's my experience that when I took two drugs at once, it created different side effects entirely than I had on each drug alone. So for her aggression could have been the two drugs together, or one alone.
There are lots of parents in here struggling with lots of issues, so you've definitely come to the right place. Robin has a daughter about your girl's age. I'm betting Robin will chime in soon.