In To Kill a Mockingbird, how is Aunt Alexandra "the last of her kind," and how is she described in the novel?

Aunt Alexandra is the picture of Southern womanhood. She could be considered antebellum, as many of her societal values are derivative of the customs and mores present during and immediately after the civil war. Women were to be ladies in every respect: mannerly, feminine, graceful, and when necessary, steel-willed.

It is her personality and her sense of propriety that makes Aunt Alexandra the "last of her kind," as the south of her day is rapidly passing even in the 1930s, and the area is slowly becoming more open-minded. The expectations for girls, in particular, are quickly becoming outmoded and obsolete, and Aunt Alexandra doesn't quite know how to adapt.