If Richie is the book's villain, Eleanor's mom, Sabrina, is his primary victim. She's not easy to pin down. On the one hand, she's been treated horribly by both of her husbands, leaving her with a metric ton of emotional damage, nut on the other hand, she was the one who made the terrible decisions that led to those marriages. And when it comes to Eleanor, her priorities seem pretty messed up, to put it mildly.
Sabrina is a beautiful woman, and from all descriptions, was probably drop-dead gorgeous before her two horrible marriages:
When Eleanor was a little girl, she'd thought her mom looked like a queen, like the star of some fairy tale. (4.24)
Unfortunately, though, Sabrina's fairy tale turned into a nightmare over the years.
It's implied that Sabrina might have married Eleanor's biological dad because she got pregnant as a teen—we're guessing with Eleanor—and Eleanor's memories of her mom's first marriage are of lots of parties, drinking, and pot, with lots of music playing. Eleanor recalls:
When Eleanor's parents were still together, there were always people around. There were always parties. Men with long hair. Women in long dresses. Glasses of red wine everywhere. (34.69)
Her mom used to cook a lot, and somewhere along the line, had Eleanor's siblings Ben, Maisie, and Mouse. Eleanor's dad seems like a real jerk, however, and never cared about the kids—he was into drinking and gambling. We're not really sure why that marriage ended, but we can guess.
Enter Richie. Sabrina, alone with four kids, must have been desperate, but though he showered her with compliments initially, once they were together, he proved to be a monster. When Richie showed up, Eleanor was twelve, "and she couldn't imagine a guy screwing her mom over worse than her dad had. She didn't know there were things worse than selfish" (34.77-78). Unfortunately, Eleanor promptly learned this lesson in spades.
Throughout the book, Eleanor gives us evidence that Sabrina is physically and sexually abused. Almost every night, she hears her mom screaming and crying, hears the noise of bedsprings, and sees bruises the next day. Richie prohibits her mom from driving, keeping her completely isolated and without friends. For her part, Sabrina thinks only about pleasing him in order to avoid punishment.
Richie seems to hate the kids' very existence, so Sabrina buys them clothing and other essentials behind his back:
Her mom had become some sort of genius double agent since she hooked up with Richie. It was like she was keeping them alive behind his back. (22.184)
Sabrina tries to figure out ways for Eleanor to bathe in safety (which has terrifying implications), and though she ultimately ditched her, Sabrina's also the one who hustled Eleanor out of the house and away from Richie's line of fire over the typewriter incident.
That Sabrina abandoned Eleanor with those neighbors for a year, not even calling her for six months straight, is truly terrible parenting. And Sabrina always takes whatever money Eleanor finds for her, and doesn't thank her at all. At one point, Sabrina tries to explain:
"I have to think of myself. In a few years, you'll be on your own, but Richie is my husband." (32.40)
In other words, Eleanor might be her daughter, but when push comes to shove, she is on her own. Interestingly, in one telling conversation with Eleanor, Sabrina implies that all of her trouble stems from her inability to be alone. She tells Eleanor that she's "smarter than I ever was […] And braver. I haven't been on my own since the eighth grade" (43.84). Sabrina is so afraid of being alone that she stays with someone who regularly abuses her.
Do you blame Sabrina for her actions when it comes to Richie? It's a complicated issue, and one that doesn't really have a clear answer.