What are some quotes by Selina that show how she values beauty in So Big by Edna Ferber?

The protagonist of Edna Ferber's novel So Big is the formidable Selina Peake DeJong, for whom life is very difficult indeed. Scarred from struggle, Selina often finds herself in "a trackless waste," her best efforts to find an earthly paradise notwithstanding. But even when she is at her lowest, she uses her aesthetic imagination and innate sense of hopefulness to see things differently:

But always, to her, red and green cabbages were to be jade and burgundy, chrysoprase and porphyry. Life has no weapons against a woman like that.

Ferber says that life lacks weapons against Selina because it cannot defeat her spirit. But the mere fact that life requires weapons in order to see things as beautiful indicates that the world of the novel is a world at war, in which the vision of beauty must contend against the reality of ugliness, poverty, scars, and loss.
Selina's vision of beauty, it should be noted, is not a vision of inhuman perfection but rather of a beauty tempered by the shadow of suffering:

“Any piece of furniture, I don't care how beautiful it is, has got to be lived with, and kicked about, and rubbed down, and mistreated . . . , and repolished, and knocked around and dusted and sat on or slept in or eaten off of before it develops its real character,” Selina said.

This shows that Selina's aesthetics are related to her sense of character; with human beings, as with pieces of furniture, Selina values what has endured through trials and misfortune over and against that which is untouched.
In a discussion with the character of Dirk, Selina warns him against abandoning the restless pursuit of beauty. She warns him against settling for safety.

Suddenly she raised a warning finger. Her eyes were luminous, prophetic. “Dirk, you can’t desert her like that!”“Desert who?” He was startled.“Beauty! Self-expression. Whatever you want to call it. You wait! She’ll turn on you some day. Some day you’ll want her, and she won’t be there.”

In this passage, beauty is almost an anthropomorphic deity—if she is abandoned, she will flee. Here, Selina assumes the role of a prophetess, warning against succumbing to hopelessness and mediocrity. Her vision for Dirk is of an impoverished future, in which one day he will turn to beauty again in hopes of inspiration, and she will not be there.