eatsleep makes a good point about friction between her teammates. She isn't a senior and I could see the other players questioning her commitment to the team. From your description it seems she is a key player to their team and her absence would definitely be felt. However, I do understand how hard this must be for her with the whole boyfriend thing (it makes them loopy ;D), but in the long run, my guess is she will pay more in consequences for missing the game, than if she talks to her boyfriend and goes on Saturday with him instead.
As far as the coach honoring his word, that's a tough one. I don't think you can say he's a bad guy for not just letting her go. His job is to make sure the team is prepared to win every game, and with tournaments right around the corner, it is extremely common to pick up games to keep players sharp and focused. He doesn't make decisions about scheduling a pick up game based on whether he told one player she could miss practice or not. He's looking out for the best interest of the whole team.