Here's how I see it.
I had originally thought of her as a schemer to take ownership of the Conclave, something like gaslighting Suspiria until she did it for her.
After all of this, she would be like "Suspiria did it, look, look!" I also suspected Bell (as I say, always the quiet ones) did alot of mind-control stuff and was way stronger than the Conclave originally believed.
And yet, a person who realizes that they aren't legitimate, means... they would have committed an act in full view that it would gain them nothing and cost them disgrace. Qtalda could simply have allowed everyone to believe she is dead (she's invisible after all), and the others Crest was talking to would be like "Ummmm she does have parents, it's possible everyone was brainwashed." The blame would still entirely be on Suspiria, but Qtalda could be a secret joint leader and Bell would ostensibly be the official admin of the Conclave. Nobody would even know she's still there (literally), and this is all it would take for her to get away with her plans. Instead, she refuses power, and openly admits that she is still alive.
That's not "part of a longer plan" that's sabotaging any plans you might have.
This is not to say she is not, as Suspiria puts it an "evil bitch." But as things go, neither the Thin Man (more of a
Cloudcuckoolander scientist type) nor Suspiria (too powerful and unstable for her own good) nor even Qtalda are what you'd call stock villains.
Omae wa mou shindeiruUpdate: Yes, she'd rule exactly like this, if she were trying to takie over. Publicly assign someone else and pull their strings. Exactly like... uh oh.