Indeed. It is not so much a nerf but a flawed design. Willow can't enter the ruins or hardly farm nightmare fuel. In the summer/autumn you have no idea when you suddenly freeze and take damage if it is because of her sanity or wetness or temperature. This is only confusing.
Please, Klei, remedy this. Make Willow ejoyable once again. Willow's overall concept is very fun and she's a fun character to play but the random freezing is simply detrimental (there is no real way of offsetting it either; not like the other disadvantages for other characters).