OK, now that I read your post I understand that I may have miscommnicated why this is bothering me.
I'm bothered because I am expected to be there, but the hostess has made no effort to contact me directly regarding the party.
Basically I would like to give my aunt the message that if she wants my attendance, she needs to tell me so herself. Invitations by proxy annoy me.
I get that, completely.
But again, just meet it head-on. Before the mass email, I'd say you should call or email and say, "Aunt, I'm sort of confused--all these people are expecting me to attend, but I haven't heard anything from you directly at all. I don't have info, and I'm not absolutely certain I'm invited. I want to be sure--do you have all my contact info? Let me give it to you. And I wanted to ask you to directly contact me about these sorts of things instead of assuming someone else will tell me. That's not safe, it doesn't make sure I get the info, and it leaves me wondering if I'm invited."
And then you do that every single time.
And you also say to your mother, "In the future, please tell Aunt, 'Did you tell Shopaholic? She's a grownup now and she needs to get her invites directly. Do you have her email?' "