Good point on the fencing. I was thinking collision at the plate, not fencing. I do prefer it to stay on all the time.
To be honest, thinking about her two tournaments thus far this year, I don't think I have seen her with her helmet off during play. So either there have not been many pop-ups behind the plate (the ones I remember were bang bang plays trying to dive for the foul ball-no time to take off the helmet) or the coach has decided not to press the issue.
I've seen multiple times where a catcher pulling off her helmet cost her the little bit that prevented her from making a catch. I have yet to see one where the player missed the play because she didn't pull off her helmet.
As I mentioned before, reading the trajectory off the bat is the critical moment. If they miss that, it's hard to recover from, helmet or not. A few times, I've seen pop-ups straight up where the catcher didn't see it off the bat, pulls off her helmet, and nearly gets hit right on the top the head with the ball.