Elevated ammonia f om Zonisamide or urea cycle disease?

My nonverbal autistic/ epileptic daughter has elevated ammonia, 41 is latest value
We have done so many tests and it keeps coming back to change from Dilantin to Zonisamide a year ago but i saw urea cycle disease raises ammonia? But doctor won't do tests for that so now looks like we need a new AED? Can't do Depakote, Dilantin, dr suggests Lamictal.
She has very few clonic tonics, possible absence seizures but also on Seroquel, Buspar..
Her T3 just slightly low, is hypothyroid but other tests, TSH etc okay
Autism/ epilepsy a lot!!
Thanks everyone for reading!