Oh, I kill the Alraune every time. Best Girl Cait says she gotta go then she gotta go... off this mortal coil.one more confession: I killed the Alrune more times than sparing her, even though it feels morally wrong.
Honestly I'd never even considered sparing her until now. If there was a quest where you could have Sanders cleanse the plant-core and uncorrupt the plants then maybe I'd keep them around, but 'dominating' the corruption doesn't seem like you're stopping the corruption so much as participating in it.