How Do I Know What I Think Until I See What I Say?

Yesterday, two things happened. (Okay, a lot of stuff happened - here are the things I want to talk about...) (1) I read on a blog - I can't recall which one - that you need to make your characters likable in the first chapter and reveal their flaws later. (2) I went to critique group. I had a moment of panic about the first thing, because my main character S is not likable in the first chapter. She's not a monster or anything, but she's been put in a situation that she hates and she acts out against it by being mean to people who are nice to her. Several of the people in my critique group were concerned about how mean she was, in fact. But making S likable in the first chapter doesn't work for the story I'm going to tell. S cannot be happy or friendly or nice in the first chapter, because if she is, then I've got no story. So that piece of advice sucks. What doesn't suck, though, is the second thing - my critique group. Because even though they were concer