Just to add to this, there's been a few hints that there's at least "two" versions of Ami.
In 'Lamb Legs' there's the Ami who breaks the 4th wall and threatens Sensei:
Then there's the Ami that shows up afterwards telling him this stuff isn't her:
Maya makes it clear that, to her, Psycho Ami and "Real" Ami are completely different:
Ayane seems to think Ami is a good actress due to switching between innocent and threatening at times:
(Ayane is smart, but kind of seems delusional:
When it comes to understanding others.)
Then there's the "Mega Ami" and Mangled Ami stuff:
And of course, there's Nao and whatever that Twisted Ami was:
Etc.
Overall: The way I see Ami at the moment is that there's "Real Ami" who seems to be the one feeling like she's being bullied, "Other Ami" who seems to be the one trying to manipulate others (likely even "Real Ami"), and then there's what Maya seems to think slaughtered everyone, aka "Psycho Ami", who I'm thinking isn't really Ami at all. Just something that used her form.
The Shapeshifter saying Ami won't touch Ayane:
Could be hinting that whatever is dangerous, isn't actually
Ami. That doesn't mean it can't take her form or something though. This is coming from a Shapeshifter afterall.
Psycho Ami could also just be a false memory used to control Maya.