I am so angry about this.

Even aside from how Autumn is treating you (and where she got these ideas)...

How is it that you know this?? Someone obviously "leaked" the information to you, strictly for the purpose of hurting you. If this wasn't about manipulation and hurt, how about "We can't come to the party today because Autumn doesn't feel well")

By "spreading the news" it not only hurts you but also others at the party.

What about the kid that the party is for???? Anyone think about that? "Your cousin(?) Autumn can't come today because she isn't feeling well but she wishes you a happy birthday" vs. "Autumn won't be here on your birthday because a petty fight that doesn't involve you is more important to them then celebrating your birthday."

GGGGRRRRRRRR!!!!