I'd like it to be where the rule book says it must be. The USA book is pretty clear, you push from the pitcher's plate and in this picture, she clearly is pushing from somewhere else. For those who think its a weak 2nd push, the book does not differentiate between a strong or weak illegal move.Where would you like that foot to be??
As far as which umpire is allowed to call it, the answer is any umpire that see's it is required to call it. That being said, it is sometimes hard for the PU to watch the ball coming out of the hand and the feet at the same time, so with 1 umpire, it probably won't be seen or called. That's why between innings when the pitcher is warming up., I usually watch from the sideline and see if there is something out of the ordinary that I should pay attention to during live play. But clearly it is hard for the PU to see subtle illegalities in the pitcher's footwork.
Hope that helps.