To answer the original question from a players perspective...I have never been 'promised' a position or a spot on a batting line up in travel ball or rec league, just a spot on the roster. The closest I've come is my college coach telling me that she was looking to replace their graduating #1 with me as an incoming freshman; but even then, I did not take that as a promise that I would be the #1. I have been promised fair playing time on past travel teams, I do believe. That's really the only thing a coach should promise..that he/she will try to give each and every player on the team innings. Nobody should pay $300 to sit the bench...but nobody should expect to start every game at their preferred position and bat #4 either, because there are so many other girls on the team that are paying the same amount and driving just as far as you are...so what...they should sit the bench and "pick dandelions" in the outfield? It's a promise a coach shouldn't ever make, and if you are ever promised that, you should know it's a lie and run far away from that coach...
If the situations you are describing are completely accurate, then I am sorry you've had bad teams, but if it's a reoccuring problem, try to take a step back and see what exactly the root of the problem is...remember that the coach has sometimes as many as 14-15 other girls that he needs to get in the game too. If right field (which is a very important role, especially in travel ball where the ball is hit hard in almost every game) is where the coach needs your daughter for that game, she should be happy that she is one of the 9 out of 12-15 girls who is getting to play and that she is not on the bench...sometimes it's hard to keep it in perspective. Also, if she gets moved down to #7 batter she should say to herself "oh man...I'm not performing as well as I can..time to hit the cages!" and work as hard as she can to constantly improve so she will be performing in the games. If she's in the cages for hours a week and is working her butt off to do better and still isn't getting a chance, then you could talk to the coach about it. But if she's performing mediocre and is watching tv in her free time, there is no leverage to complain.
I'll tell you how it works in college, though, because it's not all about fair playing time and there are no promises. Our coach tells us you could be a 3 time all american returning senior center fielder...but you don't have your spot until you beat out that awesome incoming freshman and the other 6 outfielders on the team and prove you deserve it. She also says that if anyone ever comes to talk to her about anything regarding playing time she will have a closed door. You earn your spot, and pretty much the same 9-10 girls out of 20-28 play every game...if you want a spot you need to show you want it and take it; nothing is guaranteed! If your daughter is not playing, there is a reason...it's either because she is not good enough, she is not working hard enough, or there are other girls who are just as qualified as she.