Sage: Green Eye cure research
Your research takes you wandering through several sections of the stacks - scrolls on herbalism, druidism, and the nature of Reverie.
You come to understand that the purpose of forcing the disease into a physical representation is in fact to change the dominant perception of what the disease is. When the disease was perceived as a poorly understood infection that could lurk anywhere in Reverie, it was able to affect many sleepers. If the disease has a coherent form, only those who come in direct contact with the physical representation will believe themselves to be open to infection.
Given that the cure is understood to be sufficiently powerful to help one person, it cannot be understood to be sufficiently powerful to destroy the concentrated manifestation. It would still damage the physical incarnation, to a degree at least as great as any other particularly strong magical or physical attack, possibly greater. However, in order for the cure to fully overcome the physical manifestation of the disease, something would have to be done to multiply the power of the cure proportionally to the concentrated power of the manifestation.
A librarian mentions that they heard about a Hania herbalist using a Witchwood Leaf to vastly multiply the number of sleep resistance poultices they were able to produce last winter. You are reasonably certain that one could be used to similar effect by trained hands to amplify the power of the cure. There may also be other ways of multiplying the perceived effectiveness of the cure.
Another possible way to increase the effectiveness of the cure would be to study the physical manifestation of the disease and find a weak spot: a metaphorical chink in its armor. Applying the cure to an appropriate metaphorical weak spot could have a significant effect on the manifestation. However, you can not make much more progress on this line of research without knowing more about the nature of the manifestation.