Now I'm curious as to what the concert was! Hope it was good.
That just seems so odd to me. Even if it were my best friend, if she'd made plans for a concert that involved travelling and she had made the plans before my party, I just can't imagine letting myself say anything more than 'oh, I'm really sorry you can't make it, you'll be missed'. Did she expect you to realise, after weeks of passive aggressive remarks, "Oh, I DO want to go to your party!" I do not understand that mindset at all.
In my view, I only want people at events who really want to be there. We've had issues in our group before with people who come to a planned event and then make it *really* obvious they don't want to be there, and it's such a chore, and so on. This, to me, is so much ruder than telling someone you can't make it. For any reason, even if it's "I want to play games on Facebook and play with my cat."