Can a fastpitch umpire tell a catcher how to remove her helmet for a popup?

yes if when she tosses it it almost hits another person

i always spotted the ball then tosed my helmet just off to my right

There really is no rule against it unless it gets in the way of making a play and cause injury I'm right handed so when I have to take of my mask it usually ends up on the right side of me but as for an umpire actually getting upset about it as long as it doesn't interfere with the play getting made she can do a backflip while taking it off for all he can do about it just let him fuss he will have to get over it eventually

First of all, an umpire should never ever talk to players. He is not the coach. If someone breaks a rule then the umpire should address the coach but never talk to the players.He is there to officiate and not coach.

She can take her helmet off as much as she likes.

That umpire can't do anything about it.

In MLB they do it, so that ump is not too bright.

There is no such rule that REQUIRES a catcher to remove her helmet on a popup.