It just occurred to me recently that I don't think there's even much of anything related to her tadpole beyond your initial meeting with Karlach, unless I'm forgetting something. Other companions had options now and then to do something like using the parasite to peer into their mind, but I don't remember anything like that with Karlach.
If I'm correct, it is later in the game,
when you save the Emperror and he tries to convince you to accept the tadpole. Then you can ask Karlach to aslo to accept hers.
