A Quaker lady of high principles, the wife of a not-very-successful engineer, you lived in exile [...] and stayed a cultural snob through it all. (1.1.38)
Susan is one classy lady. To be honest, however, this is a bit of a mixed blessing. On the one hand, it allows her to move through society with ease and earn oodles of respect from anyone she meets. On the other, it gives her high standards that are often impossible to meet.
I think her love for my grandfather, however real, was always somewhat unwilling. She must unconsciously have agreed with his judgement that she was higher and finer than he. (1.1.44)
Although she digs him, Susan has reservations about Oliver from the get-go. These concerns center around the fact that Oliver is a little low class compared to her: he lacks that certain je ne sais quoi that you need to navigate the world of the rich and famous. Regardless, the heart wants what it wants, so Susan shoves these concerns to the side in the name of love.
A relatively poor girl making her own way—what Rodman would call "upward mobile"—she put a higher value on gentility than most who were bred in it. (1.4.12)
So, this is why Susan is so concerned with acting fancy. Because she grew up poorer than most of her peers, she's pretty much obsessed with trying to fit into the cutthroat world of high society. For the trust-fund kids she parties with, however, this lifestyle is something in which they were born and bred to take part.
The Wards had not chosen to live at the Hacienda, where things were rather more civilized and where people would have had a better chance at their company. (2.1.131)
Despite her preference for luxurious living, Susan never really bonds with the rich businesspeople who own mines in the West. It makes sense when you think about it: these hard-nosed businessmen are nothing like the literary intellectuals she rolled with back in New York. Class isn't always about money—sometimes it's just about, well, class.
It was clear to him that, however she tried to reassure him, Susan carried his failure home in her baggage. She returned East poorer than she had come West. (3.6.5)
It seems like all of Susan's fears have suddenly come true. She doesn't actually seem all that concerned about living in poverty, though—she seems much more concerned about how her friends will judge her when she shows up in shabby clothes. But, how good could these friends really be if they would throw her shade over that?
She saw that he lacked some quality of elegance and ease [...] that these others had. It seemed to her that he sat like a boy among men. (4.5.39)
That's harsh. As time goes on, Susan's concerns over Oliver's lack of class grow even bigger, making her forget all of the reasons why she fell in love with him in the first place. It's actually pretty sad. Still, Susan has made it abundantly clear what's important to her.
Somewhere back in her mind lurked the figure of Thomas Hudson, in shining mail. His example dictated my training as it had dictated my father's. (5.1.4)
Whenever Susan complains about Oliver, what she's really doing is comparing him in her mind to Thomas Hudson. But, would she really be happy with a dude like Thomas? We're skeptical. Either way, he provides an example that's impossible for Oliver to live up to.
Susan understood that her husband's name was to be mentioned and passed by, not dwelt upon; he was to be walked around like something repulsive on a sidewalk. (6.1.30)
While Thomas is Susan's ideal masculine role model, Augusta is her ideal feminine role model: she's the most ladylike lady who has ever ladied. Because she respects her friends so much, it crushes Susan that Augusta and Thomas don't seem to like Oliver very much. (We, however, can't help but wonder if Susan's concerns are all in her head.)
"When I was first at New Almaden the sight of a Chinese made me positively shudder, and yet I think we all love this smiling little ivory man." (7.3.82)
First, we have to call out Susan for being racist. But, the important part here is that she's able to get over these small-minded prejudices by becoming a friend to a Chinese immigrant. If only she could be so open-minded about issues of class.
"Right now he was told to stay in and work at what he's weak in, and he's out irrigating. At this rate he'll never get into a good Eastern school." (7.4.67)
In the end, Susan never stops being that classy lady we've always known her to be. She still values literature over hard labor. She still values education over on-the-job training. And she still worries that her husband isn't good enough for her. Even if we disagree with certain aspects of these beliefs, it's a bit naive to think that she'll change them overnight.