So this is my theory all about (in my opinion) one the most controversial characters in the RWBY fandom. You either like her or you hate her. I myself am in the like camp. (I mean c'mon my main RWBY OC is best friends with her.) So I think Cinder is going to get redeemed, Why? Because I don't think what she's doing is her own fault. I think she's being controlled. More specifically by the parasite Grimm in her glove.

This thing in case you don't remember. Anyway  after Cinder steals a portion of the fall maiden powers, the glove (and the Grimm) are absorbed into Cinder's body giving her the tattoo on her back. So here's where my theory comes in. I don't think Cinder was ever evil just very misguided. She wants power. Why we don't know,  but she does. Before she stole Amber's powers Cinder was manipulative yes but I wouldn't say she was evil. She couldn't even convince Adam to work with them even with all her charisma and charm. It took her having the maidens powers to do so. Once she had the Grimm in her she became under Salem's "spell" I guess because Salem controls the Grimm so in my opinion that must mean she's able to control the Grimm in Cinder's body. Now let's fast forward to volume 4, Salem told Cinder "don't fight it." I think she was referring to the Grimm inside her. Now let's talk about Cinder's battle scars from the fall of Beacon. I think that if the Grimm hadn't been in Cinder then it would've killed her. Think about it. The left side of her body is the one she covers and it's her left eye that's missing. Her right side is fine. The right side is also where the grimm was. I think Salem is ultimately who saved her. But because the Grimm was only on the right side of her body then she could only save that part of her body from getting hurt by Ruby's eyes. I mean think about it, Salem wouldn't want her fall maiden to die before she got the relic. How Salem was able to save her I don't know but I definitely think it's because of the Grimm. Salem's control is what's making her do all these terrible things that I don't think she would've done before hand. So I feel that if the Grimm can be removed then Cinder will be on her way to a redemption arc. But I think to do that Cinder has to let her lust for power go because ultimately that's what's allowing the Grimm to remain in her. As to why it's remaining in her is because of cinder's insane lust for power, this is causing negative energy which as we know the Grimm are attracted to.