Skinful of Shadows, a

Frances Hardinge weaves a dark, otherworldly tale in A Skinful of Shadows, her first book since the Costa Award-winning The Lie Tree.
When a creature dies, its spirit can go looking for somewhere to hide.
Some people have space inside them, perfect for hiding.
Makepeace, a courageous girl with a mysterious past, defends herself nightly from the ghosts which try to possess her. Then a dreadful event causes her to drop her guard for a moment.
And now there's a ghost inside her.
The spirit is wild, brutish and strong, but it may be her only defence in a time of dark suspicion and fear. As the English Civil War erupts, Makepeace must decide which is worse: possession - or death.