The key to the behavior is that you can not act in a way that distracts those around you.
Yes, she was young, and yes she has every right to be excited but her excitement was distracting to others and that is beyond any level of appropriate behavior.
When you act in a way that takes away from the experience for others, you have crossed the line.
Each of us is entitled to react in our own way, while I still think there was a bit too much of an attempt to make the evening "about me" from many in the audience, instead of about the talented actors and the event created on the stage. That said the only place that I feel it is inappropriate is when it becomes a distraction to others, and that is the issue here.
I stand corrected, you are as vapid as they say.