Before we meet Miss Whitlaw in Chapter 6, we as readers might anticipate that she is nasty both inside and out. After all, with the exception of Mr. Alger, Moon Shadow's experiences with "demons" (white Americans) haven't been very positive. Laurence Yep sets us up, too, with the title of Chapter 6 of "The Demoness." We immediately understand that whoever this landlady is, she's going to play a big role, for better or for worse. So Moon Shadow cleans up and wears his protective necklace when he and his dad go visit Miss Whitlaw. And she turns out to be pleasant and warm, much to Moon Shadow's surprise. He immediately compares her to "the Listener, She Who Hears Prayers, who refused release from the cycle of lives until all her brothers and sisters too could be freed from sin" (6.32). In other words, Moon Shadow's likes her instantly.
This comparison to the Listener turns out to be a foreshadowing hint from the author that Miss Whitlaw is a team player, and she's playing on the Lees' side. Or maybe that's too simplistic: Miss Whitlaw is kind of beyond sides. Over and again, Yep gives us examples of how open-minded and thoughtful she is to others: from the little things, like withholding sugar and milk from the jasmine tea, to the bigger things, like standing up for the Lees when the soldiers come to take the Tang people from Golden Gate Park.
On one level, we could say that Miss Whitlaw is accepting of people and ideas that are different to hers. On another level, we could also say that Miss Whitlaw acts from a deep and warm heart that isn't even concerned with sameness or difference, but about caring for the well being of the people around her. She runs a home for elderly people, for example, and she is an absolute superhero in the wake of the earthquake. Indeed, we might say that Miss Whitlaw is more open-minded than Moon Shadow, since he has lots of assumptions about the supposed differences between Tang people and "demon" people.
Miss Whitlaw is also a provocative character because she is a double minority in terms of Moon Shadow's world: she is not a Tang person and she is a woman. She is the prime example Yep gives us of the need to think outside of imagining "Chinese" and "white" as opposites. Miss Whitlaw might be the "superior woman" that Windrider says, but we suggest that Miss Whitlaw is just a superior person, regardless of race or gender (9.193). After all, Moon Shadow early on has the feeling that he and Miss Whitlaw were family in another life; well, we see that they form a family in this life, too.
There's quite a bit we don't know about Miss Whitlaw, such as the details of her family, or what's up with the boarding house/convalescent home. These unaddressed parts of her life remind us that this story is told from Moon Shadow's perspective, and further suggest to us that Miss Whitlaw does not talk much about herself.