Titration down from zonisamide to Lamictal

Well my decision to take my autistic, nonverbal , epileptic daughter from Zonisamide to Lamictal begins.. her abdominal distention, hospitalization, brought me back to original concern that 25# weight gain, ammonia, kidney values increased first began after Zonisamide initiated so only way to know is change
Question, from 300 to 200 to 150,100 finally to 50 .. dr will start Lamictal at 50 mg week.. then from 25-100 for 4 weeks till lab for Lamictal
Any ideas on this titration schedule?
She hasn't had seizure since 5/2022 on Dilantin..
Also her abdomen still distended.. dx at hospital discharge was bladder infection and fecal impaction, no gi visit yet, waiting!
Thanks