Got the quest from the sickly fella in the tavern. Went to the merchant lady - said to collect 3 items. Got the rotten fish and the unripened seed. However the Fire Kelp Extract cannot be purchased from the vendor in the Kings Coffin. She has no extra dialog options, and sells no such item.
Is there a way to just spawn the item into my inventory? Impossible to complete quests is an extremely frustrating issue..