It's worth noting that Sam still has an immense affection for her father, and she never blames him for abandoning the family (in fact, she doesn't blame anyone). Is it possible Sam's mother found out that her husband was abusing her and that was the real reason they divorced? If so, it would make Sam an Unreliable Narrator when she tells Lincoln about her sad pastnote .
On page 130, as Sam is about to consummate the act, Lincoln makes one last plea for her to stop. But Sam is really obsessed with Lincoln (it's not sincere love, since she's drunk) and says that even if everything is cleared up and she is exonerated, it won't bring her father back. Then she rapes Lincoln. It's pretty clear that she has a strong obsession with her father, and that she abuses Lincoln to fill the big hole left by her father's absence. It's as if having sex with Lincoln could rescue the pleasure she felt in having sex with her own father.