How about this twist?
She isn't evil, just insane? Everyone keeps saying Blackguard like its a done deal, but Rich is too smart for that. I think he has proven a couple of times that he knows how to set things up and then yank the rug out from under the most popular theories. I would imagine that, yes, at some point there is a redemption, most likely at the expense of her life, but to fall all the way, its been done to death (pardon the pun).
Going nuts and still crusading for 'good' and 'right' ala Don Quioxte is a much better storyline for her to follow (And fairly unique as well), she can play hero without losing her hatred for the OotS and still remain Chaotic Neutral (An alignment so far ignored by nearly every poster). CN is the premier align for all those anaracy nuts out there, why back away from a fallen paladin going CN, but not quite all the way to CE?