What are some instances in To Kill a Mockingbird that show how a "lady" acts?
Sadly, many of the supposed "ladies" of Maycomb didn't exactly behave as a true lady should. Some of the women of the Missionary Circle gossiped and berated the African-Americans of Maycomb; Mrs. Merriweather went so far as to criticize Atticus, who paid for the refreshments. According to Scout,
Ladies in bunches always filled me with vague apprehension and a firm desire to be elsewhere.
Scout was dressed in her Sunday best, and Aunt Alexandra made her follow her around, "part of her campaign to teach me to be a lady." Scout tried her best. When she was asked if she wanted to be a lawyer when she grew up, Scout responded, "Nome, just a lady." The "ladies" laughed at that, and Miss Stephanie even cautioned her that
"... you won't get very far until you start wearing dresses more often."
Aunt Alexandra and Miss Maudie displayed ladylike tendencies during the circle meeting that Scout admired, however. After receiving the news about Tom Robinson's death, the two women put on their best faces and returned to serving refreshments, without a word to the other women, as if nothing had happened.
After all, if Aunty could be a lady at a time like this, so could I.
In an earlier chapter, Scout's Uncle Jack cautioned her about her foul language, and he asked her
"You want to grow up to be a lady, don't you?"
I said not particularly.
Aunt Alexandra was
... fanatical on the subject of my attire. I could not possibly hope to become a lady if I wore breeches.
When Calpurnia took the children to her church, she made sure that both of them were well scrubbed and that Scout was wearing her petticoat.
Perhaps the most ladylike act in the novel comes at the very end, when none other than Scout takes Boo Radley's hand and leads him back to his house.
... if Miss Stephanie Crawford was watching from her upstairs window, she would see Arthur Radley escorting me down the sidewalk, as any gentleman would.