Selina Peake DeJong is one of the primary characters in So Big by Edna Ferber, and she is a memorable and admirable character in nearly every way.

First of all, she has an indomitable spirit. That means nothing is able to stop or defeat her, and that characteristic is evident throughout the story. When her father dies (he is actually murdered), Selina is forced to support herself and becomes a schoolteacher at the age of nineteen.

Later Selina moves from the city to work on the farm she and her husband own. and the work is physically exhausting; literally, the work is backbreaking. Nevertheless, Selina is content. Even when her husband refuses to give up his old ways and do things smarter and more efficiently, she is not defeated. And even as an old woman, Selena is unstoppable. In all of her life experiences, Selina perseveres.

Second, Selina is a joyful woman, and her joy is evident is everything she does--even the hard or mundane things. She loves life and it shows:

Selina DeJong, darting expertly about her kitchen, from washtub to baking board, from stove to table, or, if at work in the fields of the truck farm, straightening the numbed back for a moment's respite... would wipe the sweat beads from nose and forehead with a quick duck of her head in the crook of her bent arm. 

Though most people would call her life difficult, Selena never sees it that way. In fact, even when she is an old woman near the end of her life, her son's secretary notes that Selina is a woman who has a joy that is far more significant and inspiring than anything the world has to offer. This joy draws others to her, and her passion for life is contagious. When she exclaims with delight that a field of cabbages is beautiful, for example, the seasoned farmers laugh at her; but that is just how Selina sees everything, as a beautiful new adventure.

Finally, Selina is content. This seems like such a simple thing, yet very few of us ever really achieve true contentment. Even when things are good, we tend to look forward and, in some way, want more. Not Selina. Whatever she is doing, whether it is teaching or doing manual labor on the farm, Selina DeJong is content. While others seek far-off adventures, Selena is content with the small adventures she experiences, such as moving from the city to the farm.

In terms of Selena's change and evolution over the course of the story, there is not much to talk about. While her circumstances certainly change, forcing her to do and learn new things (which she does in a masterful way), Selena does not undergo any real change in her character. 

It would be easy for her to get bitter, but she does not. It would be easy for her to get discouraged, but she does not. She does take some of the blame for her son's bad (money-driven) choices in life, but it does not become debilitating or crippling; she recognizes her role in his choices and is then able to move forward with her life. While she does not change, Selena does develop, and what she develops is even deeper and stronger roots in her positive characteristics: perseverance, joy, and contentment. Says Ferber:

Life has no weapons against a woman like that.