I feel that the entire novel works to reconcile Lore with the incredibly intimate and damaging rape that occurred in her past. All her experiences outside of the protecting curtain of the Van de Oests functions to give her the perspective and independence from which she can understand and come to accept what happened to her. She must reconcile her own sexual attraction for women with the horrible emotional injury that was inflicted upon her by a woman.
Sex, throughout the novel, works against this reconciliation. First, obviously, is the event (or series of events) that so damages Lore: Her rape by her mother, Katerine. "She doesn't know how to describe it. Heavy like the end of everything" (68). This is the fundamental event that makes all the future healing work necessary, and it is entirely sexual.
Even Lore's early attempts at reconciliation are damaged, and probably do more harm than good. At the age of 13, "her films fill with porn actors wearing her parents' faces...As her parents become more distant to one another, Lore brings them flesh to flesh" (135). Sexual desire has come early for her, and she needs to find a way to express it, to rationalize it in terms of the damage that has been done to her. And so she fixates on her parents. Though it is the natural choice, because of what has happened to her, it can only have made her psychological damage worse.
There are several other examples of how sex works against Lore's independence and rational thought. Among them: The scene in which Lore films her friends having sex while drugged, for monetary gain (196-7) and the continuous sex work that Lore and Spanner pursue to pay for the aphrodisiac (220, 262, etc). These events, always involving sex, always work against Lore. She cannot reconcile herself with the past when her perspective of sex continues to be corrupted by mixing it with money.
An important note: Sex between women in this novel always involves penetration, though that is not strictly necessary (235, 220, etc.). It is not the equal sharing of pleasure that it could be. Sex is inherently a violation in Slow River, I think with the purpose of emphasizing the damage that it has done to Lore. It seems that the only solution is abstinence. Lore's relationship with Magyar is very chaste and intellectual. It is based on their mutual respect, which is followed, instead of led, by physical attraction. Lore can only overcome the damage that has been done to her when she is able to feel this physical attraction in combination with a more abstract mental attraction.