Spoiler alert for the sad souls that'll try to read this.
Ok this book is dumb, guessed the end after the first 4 chapters, didn't even finish it and googled the end and there it was... The so called hints about the main character nature are so many and so obvious throughout the book that it wasn't even fun try to guess it.
From when she hides that secret bag under the bed, to when she forget her personal infos at the doc office (redundantly remarked thorough The whole scene more than once, like just say it then that she's a killer), to when she keeps saying she had needs to be satisfied before going back home, all the time.
The people that was impressed with the twist should try to read some Agatha Christie, their head would explode if they found this one surprising at all.