If Geralt chooses to side with the vodyanoi and offer Strawberry as a sacrifice to Dagon, then he must lure her all the way from her pen in the village to the landing where the Fisher King's boat is tied. He must then take her to Black Tern Island, and once there, to the altar, carefully avoiding any wyverns which might get in the way. Then he must kill her. Yes, kill poor, sweet, glossy-coated Strawberry. It is really too bad at this point that the game animation does not show Geralt with Strawberry in the boat, that would truly be hilarious.