In my opinion, what Scout has learned by the end of this chapter is that her Aunt Alexandra is a lady, and Miss Maudie probably is, but none of the others in the Missionary Circle is a lady.
What I mean by this is that being a lady does not mean being superior and looking down on other people. If you are a lady, Scout learns, you need to be caring and fair. You need to not be hypocritical like the other women who are at the gathering.
Finally, I guess, being a lady means bearing up under stress and sadness and not letting those things show.
So being a lady is pretty much like being a good person.
I think this is a great question. Everyone's definition of "lady" is likely different. I think the portrayal of the woman of the society is not necessarily embodied in either Aunt Alexandra or Miss Maudie (although they are truly admirable ladies in the chapter). What Scout learns about what it meant to be a lady in Maycomb is troubling to her and to us as readers. She learned that being a lady meant gossiping about other people. It meant acting like you are doing good, but being a hypocrite about it. It meant drinking tea and making fake compliments about how good the goodies are. It meant dressing uncomfortably to impress other people. I think this shows that the Southern woman she saw was not the Southern woman she wanted to become which is why Maudie and Alexandra's fortitude after the news of Tom's death is so important.