I would say that above anything else, the tragedy with Suigetsu is that her being 'doomed by the narrative' isn't in the sense that she's fated to die tragically, rather, it's because she's essentially concluded that she cannot conceive of a life work living... it's an existential tragedy rather than a circumstantial one.
She does not want — she holds no desires, no preferences or sense of individuality in that regard. Growth requires us wanting, yearning for something more, but Suigetsu doesn't experience this. It's almost as if she's static by design, performing kindness while not feeling it... rather than it being something like, 'in reality, she's cold-hearted and doesn't care about anybody!' it's more that the kindness she displays is a learned habit, a script of sorts that she follows. She doesn't choose her traits, or her personality, she is as she is and that's the extent of the thought that she puts into herself, her personality, her everything.
You see this acceptance in many regards, such as with her lack of self-preservation... In dangerous situations, she doesn't fight back or flee to protect herself. If she is the victim, she simply accepts that. If anyone else is, she'll step in for them, because she sees those around her as having more worth, more value than herself. You could even say you see it in her romantic relationships (theoretical here, of course), where the door to her is open, but her heart remains locked. You can get close to her, so to speak, see her hobbies, how she spends her day, she'll tell you inconsequential stories of her life... she'll listen diligently, she asks the right questions, remembers small details, she learns how you prefer to be treated and loved, but she will never fully reveal herself, even in an undeniably ideal situation. She could be surrounded by people who love her, and they can claim to see or understand her, but their love lands upon a surface that simply reflects and never holds. Or, when she does attempt to 'bare herself', I do think that the way in which she does so can be seem as deeply discomforting and even disturbing... she's a scarred woman whose come to accept the way that she is, rather than changing or pitying herself, and sometimes seeing her thought processes or unfiltered actions and words would likely push someone away if they didn't fully understand... She's willing to desecrate her very self for the benefit of someone else, and can encourage rather dangerous or extreme behavior enacted upon her as a way of showing 'how much I love you'.
At the end of the day, she's fully able to articulate herself, her emotions, her very essence of the reality of her situation, but still paralyzed regardless, trapped in a cage that she seems to only reinforce rather than escape. She's doomed because she's already accepted it, with the same placid emptiness she drifts through days with... she just endures for no benefit. Her presence is so strange that when she disappears, things will continue on without halting. She's never learned her life is worth living, and she's too hollow to discover that on her own.
