my daughter was diagnosed recently

[RobinN]

Freaking out won't help either one of you. I would think that she is safe in a car seat. There would be no way for her to be choked or hurt. So I would breath, and when it is safe to pull over do so. I personally would be talking gently if it was my daughter. I would let her know that I am there. Driving like a maniac might work a few times, but there will be the day when someone else is not watching out for you and you make a mess of the situation. Is there a song that you sing to her to comfort her? Maybe you could do that to comfort both of you. Our children hear in our voices whether or not we are paniced or not. They do want to be assured that we are in control of any situation that arises. That way they can feel safe.
IMO

[Bernard]

If you see her having a seizure when you are driving, check the clock and time it. Unless the seizure is prolonged or she has multiple seizures in a row without regaining full consciousness, there is no need to pull over to the side of road (assuming she isn't banging her head into the window or car door).