TheWeirdoAgain60
Try to find a better club and dump this ''leader''/awful child.
Tell her in front of everyone else in the most patronising and condescending voice you can ''Oh, poor little (whatever her name is) needs a nap and a change of nappy''
That should make everyone else laugh while embarrassing Little Miss Bossy!
No point in responding to someone else's bad childish behaviour with similar behaviour oneself. Imo that could lead to people saying "6 of one, half a dozen of the other" type comments. Many people would respond badly to you if you act like a child yourself - most likely by shuffling off away from the pair of you in embarrassment and looking for a more "adult" and classy group.
Nope.
Just either walk out of the bookclub (and do tell people why you have) or continue going - but take Mrs Leader to the side and ask her straight why she was making those faces and say that you feel disrespected by her having done so and that the leader is supposed to have an objective impartial take on things and whether she will be doing so from here on in, that all views on a book are equally valid and requesting her assurance she will stop making faces. There is just a possibility you misinterpreted her face - and that gives her a chance to give another take on what was happening (though I'd say there's a greater chance she did mean it....but you've covered all angles at any rate if you do that).
You could start this talk with her by saying something like "Maybe I'm misinterpreting and you didn't mean it that way - but it looked to me like ***** and can I have your take on what was happening here?" That way you've acted like an adult and classy etc. I would say you'll embarrass her if you were right and she was indeed acting like a child/biased observer/whatever.
Basically - that is what I see as your options.
There are a lot of Queen Bee types around and it could be that she's one of them and it's her way of keeping herself "at the top of the hill" to act this way - but asking her, as I suggested, makes it plain you know everyone is equal and you're wondering what is going on.
It may well be that you have to leave - as it becomes clear she did mean it and has no plans to change. But you will have reduced her "audience" if you do so - and a Queen Bee cannot be a QB without an audience and you would have removed part of her audience from her.