Don't sweat it 4feathers. If your sister wants to accompany you to a meeting - whether it's to support you, explore her own drinking, or for whatever reason - take her along. I can't imagine that anyone would deny her presence if she doesn't say she's an alcoholic. She can choose to introduce herself as a visitor or first-timer or not....it's up to her.
There are many thousands of people who walk into AA rooms every day around the world who are not sure of anything about themselves. I highly doubt that each one is scrutinized to make sure they belong there....even at closed meetings!
Go and have a nice time. AA is certainly NOT an exclusive "club."