I would strongly urge you to follow the doctors recommendations regarding the manner you switch these medications. Your daughter was on a high dose of xanax and seizure can be a withrawal symptom. Both drugs are similiar types of drugs but I don't think that necessarily means they can be swapped out for each other as you are no doubt finding out.
Talk to her doctor immediately!
I will assume this taper from one to the other is being monitored by her Neurologist, with that said, I would stop all tapering until I met with her doctor. I personally would not let a general peds Dr. do the taper.
I have to wonder?? Did you at the time the doctor said what was said about the quick med change, have a light bulb go off in you head and think This Doesn't Sound Right........I think as mothers and fathers when it comes to our children and Meds...... we really need to listen to ourselves when the white flag is raised. How is your daughter now? I see the siezure was a couple of days ago?
Have you gotten with the Dr. already with this? I hope all is well and never be afraid to listen to that motherly voice you have when it comes to your kid~~