Is This Allowed?

[Al]

I was base umpire for 8/under coach-pitch Monday night and while watching for any runner leaving the base before the batter hit the ball I noticed one girl stepped off of first base after the ball was pitched and was only about half way to the plate. That would be easy to call, but before the ball gets to the batter she is back on the bag. I was about to call her out for leaving early, but then I saw her take a step back and get back on first base before the ball arrived to the batter. I then thought to myself I think I should have called her out even though she got back on the base. So on the very next pitch she takes a step off the base again and I call out time ... "the runner on 1st is out for leaving the base too soon". After the game the coach said she does that all the time and no ump has ever called her out. It happened to be his daughter and he happened to be an assistant for a coach-pitch team I coached two years ago. He went on to say all she is doing is changing which foot she is going to lead off with. I said to him she is not allowed to leave the base till the ball is hit by the batter and even if she gets back in time she still left the base before it was hit by the batter.

So now I'm second guessing my out call, but believe I am right. I want to know what is proper should it happen again. Anyone that knows for sure please let me know. ...Thanks, ...Al