Literally flick the control stick the opposite direction and let it set back to neutral then click B. If to fast its a missile. To slow and you won't turn around. Try it in training mode, took me ~10min to get it down as second nature.
+Talos21 For some reason your comment didn't show up. You're right, but it doesn't change your momentum like a B-reverse. That's why I said she couldn't. I wonder why the developers didn't make it change her momentum, though...