ha ha! Found it! The memory address with Empyrea's flight direction is 203A20F4. The value stored in that location is a floating point type and represents Empyrea's heading angle (in radians). A value of 0 points Empyrea due south (which I think explains why she is defaulted to pointing south when you initiate flight). A value of pi points Empyrea due north. A value of -pi also points Empyrea due north.
Ahhh, it feels good. I am totally able to change this value to correct Empyrea's heading on the fly.
This is fun. Now I think I will try to find some other useful parameters like flying altitude to see if I can push her higher than the game's typical maximum altitude. Depending on how much luck I have here, I could theoretically plot her entire course across the worldmap via a CheatEngine script (and could peg the time of day to be mid-day constantly).
Anyway, thanks again for steering me in the right direction Erdrick!