Susan Norton is a small-town gal who wants to get to the big city. That seems like a big part of what she sees in Ben Mears. He's a famous author; he's exotic, cool, and not not not from 'Salem's Lot. When Susan tells her Mom, "I know exactly what I want. Ben Mears" (9.54), she's not just saying she wants Ben Mears. She's saying she wants no part of her mom's plans, which, Susan says, are as follows:
[Y]ou can't feel your job is complete until you see me married and settled down to a good man you can put your thumb on. Settled down with a fellow who'll get me pregnant and turn me into a matron in a hurry. (9.51)
That's not what Susan wants, though. She wants out of this crummy little town. Thus, in describing Straker, the vampire's evil assistant, she says:
"I was attracted to him in a mildly sexual way, I guess. Older man, very urbane, very charming, very courtly. You know looking at him that he could order form a French menu and know what wine would go with what, not just red or white but the year and even the vineyard. Very definitely not the run of fellow you see around here." (9.157)
Sophistication, urbanity, older wiser man, "not the run of fellow you see around here." What Susan responds to in Straker is at least in part what she responds to in Ben. She's looking for someone who will take her away from all this.
And that's exactly what she gets. Barlow, the Austrian vampire, ancient beyond reckoning, who drinks only the most specialized kind of wine, and who is certainly "not the run of fellow" you find in 'Salem's Lot, takes her as his own in an extremely foreign kind of way.
As a result, Susan gets her fondest wish and becomes… nope, not a cheerful mom, and certainly not the wife of a good man, but a woman of the world, whose very face shows her cosmopolitanism. Jimmy Cody thinks she reminds him of underage prostitutes he saw in Saigon who had "a knowledge of the world that had come too soon" (14.326). And the novel describes her as follows:
In life she had been a cheerfully pretty girl who had missed the turn to beauty somewhere (perhaps by inches) not through any lack in her features but—just possibly— because her life had been so calm and unremarkable. But now she had achieved beauty. Dark beauty. (14.326)
This is meant to be ironic: Susan has attained her dream of transcending 'Salem's Lot only by dying. But at the same time, the novel does seem, almost despite itself, to get behind Ann Norton's position. Susan rejected small town wholesome values, and so she ends up a fallen woman, a prostitute who has lost her soul.
That seems like a harsh fate for someone who just wanted to date an author.
Susan's fate seems doubly harsh, since she had to give up that author—and since she didn't even get out of 'Salem's Lot. Despite her entanglement with a foreigner, Susan does what her mother wants: she stays in the Lot, among her friends and neighbors. She even reconciles with her mom, to some degree, if feeding on her mom's blood can be considered reconciling.
Susan's corruption is the corruption of the foreigner, who goes against homey small-town values. But her fate can also be seen as the victory of those small-town values themselves. They suck out all her ambitions and her hopes and leave her dead-in-life in the same old town, the one that she hoped, futilely, she'd someday leave.