Crypt of the Moon Spider

A young woman, committed to an asylum, undergoes a bizarre treatment that unlocks a vast well of power in this cosmic horror novella, perfect for fans of T. Kingfisher.
Veronica Brinkley has been committed to The Barrowfield Home, run by Dr. Cull, to treat her depression. The institution is built on the crypt of a giant Lunar Spider, tended to by a monastic group of worshippers called the Alabaster Scholars. Dr. Cull is using the lunar silk from the dead spider to "repair" people's brains.
As Veronica's memories are tampered with, she finds a surprising reserve of power within herself, upending everyone else's plans for her and stepping into a grand new role she had never imagined for herself.