I would definitely get a consultation about the dosage. Phenobarb is a very potent drug with lots of side effects. It is a barbituate and the symptoms you're seeing are consistent with the side effects of barbituates. You'll need to be careful, though, since she's already had a seizure at the high dose--lowering it will be a balancing act between the side effects and seizure control. But I'd definitely talk with a vet
As to whether you can get a decent second opinion at the same clinic, I guess it depends on the clinic. But the idea that they started her out at a high dose because she was having so many seizures is very logical--they may be intending to lower the dose as time goes on. At least at that clinic, they'd have all her medical records and be aware of her history.
that you get some good news.