Slap hitter changing from Left to right side

[MarkPSkins]

I searched for something covering this, but could find nothing. In an NFSA tournament this past weekend we had a batter called for interference in this scenario. I would also like any thoughts on ASA and NFHS.

Batter was taking signs from third base coach while standing outside the left side batter box. The pitcher was waiting on the rubber. Was the umpire's hand up? I don't recall, but IMO it should have been. Never-the-less, the batter's sign called for her to turn around and bat from the right side. She walked between the catcher and home plate and the PU called her out for interference. No pitch was ever thrown. Matter-of-fact both coaches had to be explained to what had happened. It was not like the other teams said, "Hey!"

Is there a rule that states a batter must change sides behind the umpire. I mean this was a timeout situation and it seems awfully nit-pickey to me.