Paint it Black Square: The cover is black except for the embroidery shears.
Trigger Warning: Cutting, or self-harm, drives the whole plot.
Iseult lives with her father in London and has been in mourning her entire life. Her father keeps her dressed in black to remember her mother. The mother Iseult shouldn't know because Iseult's mother died as Iseult was being born.
But Iseult does know her mother. Her mother is inside of her, a constant, suffocating presence. Iseult can't help talking to her, or trying to make others understand, so she has never had close friends or anybody to talk to except her father's housekeeper.
Iseult knows of only one way to silence her mother, however temporarily, and that is to wound herself, either in her scarred shoulder (from a broken collarbone at birth) or any other convenient place.
The book is fairly disgusting on that point. The reader understands that Iseult has no other recourse, but the amount of blood and the description of her injuries turns this book into body horror as opposed to the gothic ghost story with a twist that's advertised. This is supposed to be some kind of commentary on Our Current Cultural Moment, but I didn't see it. Maybe you will.
I got to the end because I felt obligated to, under normal circumstances I would have stopped when Iseult starts plunging scissors into her shoulder and snipping.