What you told her, was the simple truth.
You didn't tell her anything she didn't know yet. After all, if you had wanted to choose the party, you would have; but you chose the concert, so it was already clear that "the concert wins, hands down".
(And I agree with you. I wouldn't have canceled my plans either.)
What she was trying to do, by bringing it up over and over again, was guilt and shame you, trying to make you feel uncomfortable about your decision. Coming quite close to bullying, actually. By giving her a clear answer once again to all her passive-agressiveness, you showed her that no, you were not feeling guilty or ashamed for not going to her party, especially not after the way she had been behaving about it.
That is a good thing. You showed her that her harping on it was not doing her any favours, on the contrary. Sometimes, this is needed.