No, making her completely innocent would utterly ruin her character.
If you want the audience to feel sympathy for Cinder, you need to show that she did have some agency at least.
Keep the core of the character: Give her an understandable reason for wanting to be powerful. Lost her loved ones to Grimm because she couldn't fight, was always treated like shit by those highborn idiots, doesn't matter that much. Cinder was on a search for power and that lead her to Salem. She did make the choice to work with her and was willing to pay a price for that.
But the important point is that she didn't realize what that prize was. Cinder was perfectly fine with sacrificing her friends, status or morals. After getting the Grimm she keeps telling herself that she has to be willing to do the things she does and that sadistic glee is simply how it feels to be strong, to be above the others. That leads us to V1-3 Cinder.
In her current arc Cinder learns to make use of others and all that jazzs. But she fails to kill Ruby again and gets silver'd. It's important that she doesn't loose to the Silver Eye power in specific, because that would only reinforce her world view. Team good guys wins because they have better teamwork, more manpower and are willing to sacrifice themselves for others. In short, power of friendship executed properly.
Now the Grimm is gone. Cinder is fucking pissed. Her entire world view has been shattered and kicked in the balls. Maiden powers don't work properly anymore, either because of the Grimm missing or sheer stress. Cinder can do nothing to fight back against the heroes and Salem finally discards her as useless. Cinder keeps going through her actions, frantically trying to find her mistakes and find a way back to power.