I had a high school pitcher last year that did something very similar. She was a lefty and would try to start with her left foot just touching the very right hand end of the pitching plate and her right foot well outside the pitching lane. I had her in a preseason game and my partner and I both called her illegal on several pitches and told her she had to start within the lane. I ended up having her 3 more times during the season and every game I would get her a few times on being illegal. You would think she would remember I was the umpire that didnt allow her to get away with it.
So, apparently this team did not have a coach.
Not much of one. This "coach" got mad at me when I refused to give the pitcher another ball because she didnt like the one she had after already throwing pitches with it. Explained to her that once a ball was in play, it remained in play until it either went out of play are was deemed by me to be unplayable. She insisted it was not a rule and was "going to go get her rulebook". I told her to leave her rule book where it was and she could look it up on her own time.
ASA and FED (dont know about any of the other alphabet rules sets without reviewing them) both have strict ball rotation rules. If the game is started with 2 new balls and one of the balls does not get used in the top half of the 1st inning, the pitcher in the bottom half of the inning must pitch with the unused ball. After that, when the pitcher comes out to pitch at the beginning of a half inning, they may request a different ball, however, if they throw a warm up pitch they have no made their choice and must pitch that ball until it goes out of play or becomes unplayable.