Hi and Welcome!
Our daughter was on Neurontin as monotherapy for almost 2 years and she was ages 12-14 at the time. She has/had (we hope) Complex Partial & Simple Partial seizures since the age of 9 months. I wrote "we hope" because she just had a Left Temporal Lobectom (6/7/04) to hopefully irradicate the seizures. So far, so good!
She did well on the Neurontin for a short time. We had to increase it to the max and it just stopped working, Keppra was then added. She did the Neurontin and Keppra for 2 years together. When we started with a new neurologist (Epileptologist) she removed Katie from the Neurontin and she did Keppra monotherapy for 5 months until Lamictal was added. Katie's seizures have been difficult to control over the years, and to date she has been on 7 different meds and combos of those meds.
She had no side affects on the Neurontin at all. And she was up to a large quantity/doseage twice per day. I don't know off hand what the amount was without checking her history notebook.
Good luck to you and your daughter, keep a close eye on her as you head into puberty, that is when Katie really started to have meds problems. Hormones and her menstrual cycle created a lot of seizure activity. That was the case for her, it may not be for your daughter, just keep an extra eye open.
Vicki