What you say is true, but hey. Better late than never, right? Ami is probably at her lowest point right now. She hit rock bottom and stabbed the one person she cares about most with the pair of scissors she cut her hair with in a panic attack when he tried taking them away. If there’s any better time in story to show a vulnerable, emotional and scared side of Ami in story, I think now would be the perfect time for Sel to do it.
I fumbled the image preview (that was definitely Sara, not Niki), but there’s still a point to be made there. Does Ami truly yearn for a mother figure or guardian? Is a part of her actually vulnerable deep down, after all the trauma she’s endured? She’s a teenage girl and, like Maya, it’s not as if she’s invincible.
I have to wonder about that, myself.
I think Ami, at least subconsciously, surely wants a mother figure.
It's likely why Sara was able to tame her so well, and her special bonus Ami event (Lamb Legs Happy Event) has her inviting Sara (Sana and her bro) over almost every week, with Ami saying this:
We've also seen Ami black out after her mom comes up:
Which is something apparently normal for her:
Even how Ami can't help but obey being sent to her room, dreams of her mother, talks at her grave, wears her clothes, reads her poetry, etc, seems to hint at Ami wanting a mother.
She's just usually too busy raising Sensei, and trying to keep him from making mistakes, to think of what she wants, beyond his happiness:
She's also
the Caretaker, and basically acts as Ayane's and Maya's caretaker on top of Sensei's and whoever else feels sad:
In the end though, I don't think anything can replace her actual mother in her eyes, and she probably doesn't trust anyone to do so for good reason. They'd just use her to get to Sensei.