Well, it's hard for me to get a complete understanding of it, but I don't think it's about practicing at all- I think it's related to (and please forgive me, I don't know how else to say it) your propensity to feel responsible for what others are doing. She was happy and unconcerned about her performance, and even though it was terrible (was the music terrible, or was she just disheveled?) or you judged it was terrible, it was you who felt her embarrassment, not her.
Perhaps your subconscious is telling you about boundaries?
I'm not saying these things about you, I'm seeing them from the contents of your dream. And of course, as always, I could be completely wrong.