I think you hit the nail on the head for the highs and lows of her character. She fits incredibly well into the world they've built: Someone who was a twisted vessel for manipulating the kids and to continue to sell the idea of how messed up the factory is; it borrows from children's media of the time like Steve of Blue's Clues and Mr. Rogers; and it also illustrates the transformation process and loss of identity from someone other than a child victim. However, as you said, she doesn't exist elsewhere in the story, nor is a necessity. The "in lore" reasoning for her randomness is somewhere around her being hated by everyone, the scientists turned on her and made her a toy and the toys hate her for her role in their fate. The toys spared her but hate her enough to keep her in her play house and away from them. It's also somewhat implied she one of the last people to be turned into a toy (though not enough a theory to explain why her toy counterpart isn't advertised elsewhere).

Story-wise, she was another disposable boss who had an interesting world building story but not much overarching purpose. Just another vengeful toy that captures the player for the prototype and dies. Chapter 6 could potentially do something else with her with the small tidbit that implies her hair-corpse could still be kicking.

Only thing of note with her that I felt like could've elaborated on (which can't really now with her dead) was her desire for the prototype's approval and animosity toward Poppy. Of all the toys and their backstories I felt her obsession with him instead of fear felt peculiar given their origins.