Reckoning:The Queen on Eight Legs Marching (Lorestone)

From WatchWiki

Corruption and decay and filth were grown, were spread like sickness
from the fens and dells of this place. They were led not by a beast,
not by a fell one, but by her...the One Who Walks Alone, the mother of a
hundred thousand spiders. She is a queen of web and poison.
She calls herself the Widow.