prologue
Take the herbs and Anca's instructions for the medicine.
Prepare the water — hot, not boiling and not cold.
Add three spoonfuls of herbs.
Give Esme the medicine before the Blood Mass.
Only what a source states. A quest with nothing listed is a quest whose rewards are unpublished, not one that gives nothing.
Prepare the medicine wrongly, or fail to finish the quest before the Blood Mass, and Esme dies later in the story. Side quests are available while Withering Away is active, which is exactly how players lose her.
The two sources that give the recipe agree on hot water and three spoonfuls. A third lists the same options but tabulates its outcomes out of order, appearing to mark two spoonfuls correct; that ordering is inconsistent within its own table and is not followed here.