Polly/Rebecca from The Hand that Rocks the Cradle is such a tragic and layered character and I think the most complex but also heartbreaking part of her is her relationship with her trauma, which I can't stop thinking about, so here's a post no one asked for.
(tw for talks of rape and csa)
Once Caitlyn killed Rebecca's father and the rest of her family, Rebecca ended up in the foster system where it's implied she suffered all kinds of abuse, sexual too. Due to that trauma, she then became an addict + we also find out she experienced violence at the hands of a partner, which probably wasn't an isolated incident. Essentially, this woman suffered a lifetime of pain after her family was killed. But we find out that before that night, Rebecca's own father was sexually abusing her the same way he was abusing Caitlyn. And here's the thing. That specific trauma? She is in complete denial about it.
Rebecca had everything taken from her. All she was left with was her hate and desire for revenge. If she were to admit to herself that her father hurt her, she would lose her "right" to revenge toward Caitlyn. She cannot accept that she shares her deepest pain with the person who destroyed her life and whom she hates the most. To acknowledge what her father did to her would mean having to acknowledge that he did it to Caitlyn too, and if that's true, Caitlyn would've been justified in doing what she did, which in turn would mean that the years of trauma and abuse Rebecca suffered cannot be blamed on Caitlyn. Rebecca would have to recognize Caitlyn as innocent and her father as the monster he was, and she cannot bear that, because that's a scenario that leaves no space for revenge or catharsis or the warped justice she is seeking.
Rebecca's father is dead. He can never pay for hurting her. But Caitlyn is alive and (from Rebecca's pov) thriving, and her actions indirectly caused a lifetime of pain to Rebecca. She can pay. She can be the monster who hurt Rebecca whom Rebecca can get revenge on.
And she is so devoured by her own hatred and need for Caitlyn to be the sole cause of her suffering that, to feed that need, she completely shut away what her father did to her. Of course she refuses to admit that Caitlyn is a victim: she cannot admit that about herself.
And how could she? Rebecca's last image of her father isn't that of a monster. It's him burning alive while her mom and baby sister die screaming. That's what's seared in her brain. What was, in a way, a liberation for Caitlyn, was for Rebecca just another source of trauma. Caitlyn killing her father took away any chance for Rebecca to heal from what he was and what he did to her. In a way, it gave him the status of victim and deprived Rebecca of it.
Also, it's not as simple as Rebecca not believing Caitlyn imo. I think there is a resentment there. Who knows for how long Rebecca kept quiet about what her father was doing to her. She carried that pain in silence. Caitlyn didn't. And because she didn't, Rebecca lost everything. It's like Rebecca looks at Caitlyn and thinks: "I was quiet, I endured. You couldn't and because of your selfishness my baby sister who was innocent died a horrible death and I spent the rest of my life suffering."
Caitlyn told people, and eventually she was believed and supported. Rebecca can never know if they would've believed her. She was condemned to more silence and more abuse. And that silence turned into denial. She made Caitlyn into a monster and put her real monster into a box.
Maika Monroe is a phenomenal actress, she is so good at expressing emotions, but here she plays Rebecca like there is nothing behind her eyes except in the final confrontation. It's brilliant. You really get the sense that this is someone who put her pain away, put every emotion away, except hatred.
Even when Caitlyn finally confronts her, Rebecca remains collected at first. She accesses her pain through her rage toward Caitlyn, but only the pain that started the night Caitlyn burned her house down and killed her family. What came before, the real evil, she locked it away. Rebecca suffered so much that she doesn't have the capacity within her to process that her father raped her. Because of everything that happened after that night, all she could do was shut the truth about her father inside a box. She didn't have the tools to deal with it.
And that's why, when Caitlyn tells her she knows that Rebecca's father abused her too, that her father told Caitlyn about it, it shatters Rebecca. That box breaks open and just look at her reaction.
Rebecca's entire existence was revenge, and that revenge was predicated on the denial of this trauma. But Caitlyn's revelation makes it impossible for Rebecca to deny it any longer. Her father abused Caitlyn because she looked like Rebecca. It's undeniable, and it is unbearable.
What's fascinating is that Rebecca sees Caitlyn as the opposite of herself. She insists that Caitlyn isn't a good person, that she didn't suffer, that she isn't a victim. But the truth, like the film highlights more than once, is that they are mirrors of one another. But at this point, Rebecca is so broken that she cannot deal with this truth. So she clings to her hate like a lifesaver. By trying to kill Caitlyn, she tries to kill no longer just her monster, but the mirror to a horror she cannot live with. In a way, she does that to herself.