For everyone that has a problem with knocking her out instead of killing her, you need to intiate the conversation before the fight with a character with the Scholar Tag (eg. Sebille, Fane). This gives you a specific Scholar option in the conversation, which leads to her being automatically knocked out when she goes low HP. You do not need to use knock down abilities or kill the other mobs.
In addition I had the problem that the doctor did not approach after the fight, which lead to him not being able to hold her down. I was only able to solve that by healing her up and teleporting her to the doctor before starting the operation.
Hope this helps people that might still struggle with this quest.
