Here's a thought: is it really true that she listens to you sometimes and not others? I mean, is she "good" some days because she is more obedient, or is it that on that day , at that place, what she wants is what you want, anyway? So, you are no more controlling her then than you are on the day she is bolting. she is doing what she wants in both situations, just that one happens to mesh with you while the other doesn't.
It comes down to, how connected to the bit/rein and to your hand IS your horse? fundamentally?
If she's pretty connected, then when she is more emotional, and more distracted (on a "bad day"), then you'll still be able to reach and control her. But, if the connection isn't good, (only seems good because her will just happens to parallel yours), then when her will goes far away from yours, you will realize how very little connected she is to you and the rein.