How does the author establish the painter lady as an outsider?

A large majority of the first half of The War of the Wall is dedicated to establishing the painter lady as an outsider. Almost all characterizations of her make her feel like an outsider, especially contextualized in contrast to the other characters or in relation to how they react to her.
One of the biggest ways this is done is in regards to her diet. She initially refuses food that is offered to her from the Morrison twins, and this is thought of as very rude. Later, we learn that she has dietary restrictions when Mama remarks that she "don't care who [her] spiritual leader is," implying that perhaps she is an American Muslim (a detail potentially corroborated later on when she paints Malcolm X on the wall, alongside other important African American figures). Her religion and diet are frustrating for those in the community, and it sets her apart from them.
Most of all, however, she is made an outsider due to her relation to the wall. To the people that live there, the wall is a symbol of community and communal history; in the first paragraph of the story, we are given many details of different memories the narrator associates with the wall. To the people of the town, she is coming in and taking their wall from them.
Using a wall as a way of establishing her as an outsider is clever, as walls are often thought of as a means of separating or dividing people. In the story's climax, we learn that she is actually a part of the community and is using the wall to promote black pride and togetherness, which creates a sense of irony, since the community felt so disconnected from the painter lady.