In high school softball, there is a similar Case Book play (3.6.13B) where the batter runs to first on ball three. If the umpire judges that the batter ran on purpose, the umpire could eject the batter for unsportsmanlike play. Otherwise, the umpire can warn the offending team that the next batter who does this can be ejected.
It would be kind of hard to prove that this was done "on purpose" and ejection should only be a last resort. But it is a tool the umpire has in his back pocket to address this. The Case Book play also notes that the defense is responsible for knowing the count and situation and that the advance by the runner already on base stands.
For travel ball, there is no such written interpretation covering this. If the umpire suspects that the batter running is an intentional act to fool the defense, he might make a warning at his own discretion. It would probably have to happen more than once for me to decide that this is a coached, intentional play. Before that point, again, the advance by the runner is legal, the batter is returned to the plate without penalty and the defense should know better than to throw the ball when there is no play to be had.
There is one other option the umpire has- the rules about a batter remaining in the batter's box between pitches. The first time this happens, I'm probably going to let the play stand. If it happens again, I'm going to tell the batter to get back in the box. If she does not comply within ten seconds, a penalty strike can be accessed. That would be strike three, the batter would be out and if that is a coached tactic you have probably put an end to it for the rest of the game.
The only way this can be interference on the batter is if the batter, while out of the box, actually interfers with a legitimate play by the defense. For example, if the runner on first tries to get back to the bag and the throw actually hits the batter while she is down the line, that could be ruled as interference.
