Balancing opportunity and commitment

What happens when your child has a commitment to something and then an opportunity comes up that is too good to pass up, but will take her away from her commitment?
What do you do?
This happened to my daughter. She is in an 'elite' chamber ensemble and they rehearse every Friday from 4 to 7.30pm. Sometimes, things come up that she would like to attend but she doesn't because the expectation is chamber comes first; "Friday is sacred to Chamber," quips the chamber director.

Once in a while though, as in the case of having the chance to play with Amanda Fucking Palmer-in a cabaret rock band, the decision as far as daughter is concerned is to ditch Chamber.

Maddie playing with Amanda Palmer and the Grand Theft Orchestra, Phoenix, Toronto Nov 2012

She plays and has one of the most memorial times of her life. She is completely inspired. Her instructor/chamber mistress gives her grief: "You are letting down the group,"  guilting her out with words such as, "you are being selfish. If you were playing rep in a hockey team, would you do that?"

Another occasion where opportunity knocked and daughter answered was just the other week when she was asked to help out with a prestigious orchestra (they were lacking a player) and she decided to leave chamber a half hour earlier. She worked really hard to learn in four days time, musical pieces that took the orchestra entire months to learn. She had a great experience and again learned lots- especially what it feels like to play in another orchestra setting. Again, the director was unhappy. She claimed that my daughter would not have been able to take advantage of these opportunities if it had not been for having weekly chamber rehearsals and learning to play in an ensemble.  Who is in the right? The director or my daughter?

I say both. Commitment to the group is crucial if the group is to remain elite. And yes, playing with this elite ensemble has helped daughter develop her skills and get good. Of course it has. But I think that within reasonable limits, chamber should not hinder her wider experiences playing in the community.

Why won't the teacher see this as a launching pad to other experiences and adventures- that will inspire and broaden the students love and commitment to violin? If she were more reasonable she would see that going out and garnering more experiences enhances the learning daughter is doing in chamber-by bringing those other experiences to the group. An understanding teacher would be proud of her student's achievement instead of being angry and offended. A supportive instructor would applaud the student; encourage her. Instead, my daughter is met with hostility. But commitment to the chamber should not mean enslavement.
In the long run, an inflexible hold on the members of the group ends up creating an uninspiring environment that drives the best students away.
What do you think? How do you balance commitment with opportunity?