It sounds like you might really like The Red Tree by Caitlin Kiernan, a psychological horror novel about a haunting by a red oak tree, who is its own character, of an unreliable narrator who is a lesbian alcoholic whose partner recently killed herself and a bi professional artist who rents the attic above her. The Drowning Girl is by the same author with similar themes and a protagonist who lives (not a spoiler, it's revealed in the prologue of the first one).

In a wildly different tone, Among Others by Jo Walton is fantasy, not horror, but contains moments of horror, and checks all of your other boxes. It's about a traumatized teenage protagonist who has just survived the death of her identical twin in a battle against their evil witch mother, with the aid of fairies who are in some ways the personification of the landscape and obscurely connected to it.