She can't be redeemed coz she is already dead.
But her motivations and intentions were never malicious, only clumsy and flawed in its execution. That's why Steven is so much better than his mother, he is able to learn from her past mistakes and improve himself.
While PD did do that to some extent, she didn't or at least couldn't have the opportunity to fix her past mistakes. This is made even worse that said mistakes are due to extreme power she held amplify the potential harm it causes.