I think Shiori might not actually want to eat Hinako, and is actually in love with her. It's all just a ruse to get close to her and try and help her.
"I want to kill you" usually is a poor ruse for getting close to people...
To be fair, when the person in question is full on "I have a suicidal death wish" it might not be the worst idea to be "I'm going to be the one that kills you, but not yet, only when I've decided you're worth killing." Gives them a reason to let you stick around.
This. Here's my thoughts:
Shiori doesn't actually want to kill and eat Hinako. Maybe she saw the tragedy, wants to help, fell in love with the sad nearly dead girl, I dunno who knows. What matters if she wants to keep Hinako alive. And since Hinako wants to DIE, and she's a monster, she played up to her monster strengths and abilities. Hinako is less likely to just kill herself since she learned this is going to happen. This gives Shiori time to try and make her happy, with the excuse "that will make me want to eat you". Once she's happier, mission complete.
As for the argument "but she tried to kill her best friend", Shiori has been killing every monster that gets near Hinako, and she thought that Miko was going to kill her. WE thought Miko was going to kill her. There was a bunch of freaking people in this comments section that went "oh shit is Miko actually a bad guy and she's going to do a murder?" And I think Shiori is a bit less trusting than we would be, so of course she wouldn't trust Miko.
Like I know the general energy of this thread is "Miko is best girl and should get together with Hinako", cause people like the childhood friend angle, but try not to like, crucify me for offering another angle. Like I said it's almost certainly wishful thinking, but it could go this way. It COULD.
It prolly won't. But it COULD!