I can't think of a good reason to why a shootover would be done with both hands releasing at the same time. If a gymnast just hangs on the bar and drops the arm they will twist toward, they just naturally twists in that direction. I figure, why not capitalize on that fact?
If you are saying that your athlete is sort of sailing over the low bar inverted, then she is not stretching long enough below the high bar while she swings on it. She actually establishes where she will go before she lets go, just like a flyaway. After she lets go, she should be reaching down for the bar with her arm she will twist toward. A lot of kids get obsessed with just flying over the bar, and they miss the whole point of catching the bar.
BTW...I started teaching all shootovers in the girls' natural twisting direction (even if they say they feel more comfortable turning in their piroutette direction), and they are having so much more success.