I love horror but apparently I don't vibe with a lot of recommendations I find online.
I'd seen so much hype about Event Horizon and I absolutely hated it and didn't find it scary. I just watched Late Night With the Devil and whole it was definitely enjoyable, it wasn't the least but frightening. I also just watched Let the Right One In and really didn't like it. It also was not a horror movie in my opinion.
I will say one of my favorites is Sinister or the first Conjuring. Sinister for the stomach twisting dread and suspence throughout and Conjuring for the same.
She's suffering an eating disorder. Notice how all the horror she encounters involves food or things being shoved down her throat or vomiting? Notice her hair falling out, random nose bleeds and hallucinations? Far more than that! Watch it with an eye towards anorexia or bulimia.