I gave up the possibility of doing it consistently, but what did help me is looking at the animation for cr.A and pressing C when Mai is.. well if its the animation I recall, its when she starts bringing her fan back.
You may have different results depending on the lag of your display, not sure.
Also if you can buffer the special move in at a consistent time, that sometimes helps. I was doing cr.B, cr.A, then back, down-back, down+C, down-forward, forward + D. I found it was somewhat consistent when I got into a rhythm.