Custom of the Country is a 1913 novel by Edith Wharton. I thought I had read this before, and it didn't take me long to remember it. Wharton's books do tend to be memorable for me. She's a master at building an entire world and peopling it so perfectly that it's almost as if you are there. I'd recommend anything by her as can't-miss enjoyment. You can read it online.
from the back of the book:
First published in 1913, Edith Wharton's The Custom of the Country is a scathing novel of ambition featuring one of the most ruthless heroines in literature. Undine Spragg is as unscrupulous as she is magnetically beautiful. Her rise to the top of New York’s high society from the nouveau riche provides a provocative commentary on the upwardly mobile and the aspirations that eventually cause their ruin. One of Wharton’s most acclaimed works, The Custom of the Country is a stunning indictment of materialism and misplaced values that is as powerful today for its astute observations about greed and power as when it was written nearly a century ago.The New Yorker looks at Wharton's career and says, "Undine’s story is one you absolutely have to read. “The Custom of the Country” is the earliest novel to portray an America I recognize as fully modern, the first fictional rendering of a culture to which the Kardashians, Twitter, and Fox News would come as no surprise." The Guardian calls it "one of the most enjoyable great novels ever written" and says, "Not all enjoyable novels are great, and not all great novels are enjoyable. This is, supremely, both."