In Magic Kingdom, it would depend on if I was going in for Magic Hour or on a regular day. If it was Magic Hour, I would show her Fantasyland first... then head to Buzz Lightyear.
If it was a regular day, I would head to Frontierland and either Big Thunder or Splash Mountain, which ever line is longest, grab a FP and head to the other.
At Epcot, Test Track would be the 1st... it always is for us!
At MGM, Rock n Rollercoaster! Ride, grab a FP, then head to ToT, ride, go back and use FP for RnR, then pick up another FP for ToT on your way out.
Our 1st ride at AK is always Dinosaur, but many people like to do the Safari 1st. Don't miss Festival of the Lion King, whatever you do!!!