This is slowly becoming one of my favorite books, I really hope it sticks the landing. I love the jumping in and out of the epistolary mode.
I also love the expression of lesbian sexuality in a way I don't get to see too much in fiction lately, so much I've encountered left it as a barely spoken of aspect of a character but in here it's made abundantly clear how much these characters want each other both romantically and sexually. And this is one of the many reasons I love the horror genre.