The Custom of the Country: Undine Spragg and sex

Emma Bovary, we all know, is very physical and sensual. Here’s something I notice about the protagonist of The Custom of the Country: she doesn’t seem to particularly care about sex. 
Even though Edith Wharton skips the entire courtship, seduction, and even proposal, we can tell that Undine doesn’t feel physically attracted to Ralph Marvell. She likes him enough, thinking he’s sweet, but marries him for his name—the marriage is her way to get in high society.  
She is indifferent to him, and when she realises that her husband isn’t rich, the marriage is a mistake and doesn’t bring her any nearer to Fifth Avenue, she blames him for everything. 
Look at this moment:  

“"Paris? Newport? They're not on my map! When Ralph can get away we shall go to the Adirondacks for the boy. I hope I shan't need Paris clothes there! It doesn't matter, at any rate," she ended, laughing, "because nobody I care about will see me."
Van Degen echoed her laugh. "Oh, come—that's rough on Ralph!"
She looked down with a slight increase of colour.” (Ch.16) 

That’s a slip.  
I find it interesting that, contrary to my expectations, Undine doesn’t have an affair with Claud Walsingham Popple, the artist that she meets and likes before meeting Ralph. Instead, she has an affair with Peter Van Degen (married to Ralph’s cousin Clare) because he has lots of money, and adores her. He even gives her money. 
Undine goes as far as wanting to marry him: 

“It had become Undine's fixed purpose to bring Van Degen to a definite expression of his intentions. […]
But all about them couples were unpairing and pairing again with an ease and rapidity that encouraged Undine to bide her time. It was simply a question of making Van Degen want her enough, and of not being obliged to abandon the game before he wanted her as much as she meant he should. This was precisely what would happen if she were compelled to leave Paris now. Already the event had shown how right she had been to come abroad: the attention she attracted in Paris had reawakened Van Degen's fancy, and her hold over him was stronger than when they had parted in America. But the next step must be taken with coolness and circumspection; and she must not throw away what she had gained by going away at a stage when he was surer of her than she of him.” (Ch.20) 

I keep a long quote to show that she is not physically attracted to Peter in any way, and doesn’t seem to like him much as a person—she is cold and calculating. 
Look at this moment: 

“It was the first time she had permitted him a kiss, and as his face darkened down on her she felt a moment's recoil. But her physical reactions were never very acute: she always vaguely wondered why people made "such a fuss," were so violently for or against such demonstrations. A cool spirit within her seemed to watch over and regulate her sensations, and leave her capable of measuring the intensity of those she provoked.
She turned to look at the clock. "You must go now—I shall be hours late for dinner."” (ibid.) 

The kiss is part of her act, her game. Undine becomes more scheming and manipulative over time—she knows what to say, how to strike the right note, how to use people and persuade them to give her what she wants. Is it not interesting that she feels a moment’s recoil, but isn’t too bothered about the kiss? 
Peter Van Degen is ugly: 

“He had widened and purpled since their first encounter, five years earlier, but his features had not matured. His face was still the face of a covetous bullying boy, with a large appetite for primitive satisfactions and a sturdy belief in his intrinsic right to them.” (ibid.) 

Wharton keeps talking about how ugly, how repugnant he is: 

“The foremost was Claud Walsingham Popple; and above his shoulder shone the batrachian countenance of Peter Van Degen.” (Ch.5) 

The word “batrachian” means “toad-like”. Ugh. He’s also described several times as “red-faced”. 
Actually, let’s go all the way back to their early meeting: 

“He was so unpleasant-looking that she would have resented his homage had not his odd physiognomy called up some vaguely agreeable association of ideas. Where had she seen before this grotesque saurian head, with eye-lids as thick as lips and lips as thick as ear-lobes?” (Ch.4) 

Think Jane Austen is mean? Read some Wharton. But the point is that Undine feels that way about Peter Van Degen, but has an affair with him and wants to marry him for money. She likes Popple but doesn’t get involved with him, because there’s nothing for her to gain. 
I’m now on Book 3—at this point, Undine has met Raymond De Chelles. Spoilers here and there have told me that Undine would marry him after Ralph, so I paid close attention when the character appeared. He seems to be good-looking enough, but what does Undine think? 

“What she wanted for the moment was to linger on in Paris, prolonging her flirtation with Chelles, and profiting by it to detach herself from her compatriots and enter doors closed to their approach. And Chelles himself attracted her: she thought him as "sweet" as she had once thought Ralph, whose fastidiousness and refinement were blent in him with a delightful foreign vivacity. His chief value, however, lay in his power of exciting Van Degen's jealousy. She knew enough of French customs to be aware that such devotion as Chelles' was not likely to have much practical bearing on her future; but Peter had an alarming way of lapsing into security, and as a spur to his ardour she knew the value of other men's attentions.” (Ch.20) 

Again, she doesn’t seem to be particularly physically attracted to him. As she gets to know him and see his house: 

“Chelles, at once immensely "taken," had not only shown his eagerness to share in the helter-skelter motions of Undine's party, but had given her glimpses of another, still more brilliant existence, that life of the inaccessible "Faubourg" of which the first tantalizing hints had but lately reached her. Hitherto she had assumed that Paris existed for the stranger, that its native life was merely an obscure foundation for the dazzling superstructure of hotels and restaurants in which her compatriots disported themselves. But lately she had begun to hear about other American women, the women who had married into the French aristocracy, and who led, in the high-walled houses beyond the Seine which she had once thought so dull and dingy, a life that made her own seem as undistinguished as the social existence of the Mealey House.” (ibid.) 

She’s not attracted to Raymond De Chelles as a man, as much as attracted to the French aristocracy and Raymond’s castle and money and the distinguished life she always wants to have. 
In fact, apart from a brief episode with the Austrian riding-master when she’s very young, throughout the book Undine doesn’t seem to care that much about physical attraction and sex.It is good for her, of course—something like an interest in sex and attractive men would get in the way of keeping her image and climbing to the top, but I can’t help wondering what kind of existence it is that she only cares about dresses and parties, and doesn’t have any interest whatsoever in literature, art, music, nature, people, and even sex.