It sounds like she's verbal enough for quite a bit of communication between the two of you, so I would suggest something parents seldom think of – ask her what's going on. She may need help becoming clear herself, so be patient, stay open, and try the following:
Sometime when she's not needing to go, use dolls or stuffed animals to role-play a common scenario. You might play the "child" and let her play "mom," and start doing the potty dance. Listen to what bits of wisdom or confusion emerge from your little girl's words and actions.
You may hear information that challenges your assumption that she's "decided" to wet herself. You may hear anxiety, skepticism, or anger about the new level of responsibility that's expected of her. You may discover a new solution neither of you have thought of before. Or she may see the situation from your side and set a new intention for herself.
If it is a fruitful approach, you might wish to role-play her understanding of what will happen at dance and school – plumb her feelings, hopes and anxieties about these new activities. If both are scheduled to happen at the same time, that might simply be a bit overwhelming for her. Perhaps she doesn't feel confident that she'll be able to keep up her commitment to using the potty, and so is giving up in advance.
At any rate, C., your daughter may be able to give you a great deal of information about what's going on with her. That will almost certainly help you make her next months happier and more successful than if you don't have that information.