We drove from CT to Disney with ds last year when he was just shy of 6 months. He did great on the way down, not so great on the end of the way back (though I don't remember much about the way back, I'll have to ask my DH). On the way down we left at night, basically put him to bed in his car seat and took off. He slept straight through the night no problem, just like he would at home. We had to stop to feed and change him during the day of course and let him out of his car seat for a few minutes. Whenever he was awake my DH or I (usually me cause DH drove most of the way) would go sit in back with him and entertain him and when he fell asleep I would either fall asleep too or go back up and sit with DH. It worked out great too because we got to WDW in the evening and managed to actually call on our way down (when we decided we were going to drive straight through to Disney instead of stopping in a different part of FL which would have been silly) and get a day added to the beginning of our stay and get dinner ressies for Poly during Wishes! What a great way to begin the vacay then we went back to the room and got a good night sleep and started fresh in the morning. Before that I always wanted to get there during the day and go straight to the park, but that was so much better.
The way home he was more fussy and fidgety (if I remember correctly we left during the day so there was more awake time for him in the car).
I def recommend leaving at night and doing most of your driving at night. And I think if you have enough drivers to make it safely going straight through is best because if you stop during the day and try to sleep in the hotel during the day and then start again at night the kids will be up because they slept all night and someone will have to stay awake with them. Take her out of the car whenever you stop and stop often during the day. Bring her favorite toys and go sit with her when she is awake.