I'm actually working on the same thing. I think Kendra makes a great villain in this campaign. One that's been with the group from the start. I haven't fleshed out the details either, but I like to think the Professor is not only a Professor Van Helsing type, but also a dabbler in the macabre. I'm not a fan of how the Esoteric Order of the Palantine Eye works, and I'm probably going to focus on their pursuit of forbidden knowledge. One of the gothic tropes that wasn't touched in the adventure path was Jekyll and Hyde. (At least that I can recall). So I was also toying with the fact that perhaps the professor or the order was involved in some experiments that went askew. What if Kendra actually was a test subject for a ritual or potion that split her personality? Perhaps she isn't all evil, perhaps she has an evil counterpart. This would also help with any spells of detection. Perhaps Kendra doesn't realize about her evil half? She might even actively try to track down A.A. not realizing it is herself. I'm thinking like Tristan/Malken from the "The Enemy Within" Ravenloft novel. I'll nail this down more as I develop it some more. But I think she's a good villain and will make a more memorable ending to the campaign.