So what about telling her that unless she grew up gay she doesn't know, and that it bugs you when she says it? Maybe she's just not thinking. As opposed to trying to alienate you.

Everyone has periods when life sucks, some for more or bigger reasons than others. It sounds like she's trying to be supportive, but is without clues. If you want to keep having her as a friend and not grind your teeth to dust when you're with her, talk to her about it.

Good luck with the party. I hope it's a great success.