One potential permutation of that, dependent on more assumptions than I care to count, could be that she was intended to sunder the world because that was her summoners' only solution for dealing with the problem of Zodiark spreading his influence (much like he was his summoners' only solution for saving the planet) and enacting the final stage of the Convocation's plan.
Her summoners determined, somehow, an irreducible minimum of aether that would be necessary to leave in the Lifestream (for each shard?) for the cycle of rebirth, allowing her to draw the rest to function. She is still drawing aether above that amount, leading the great bulk of souls to become ever more diluted even with each subsequent Rejoining reinforcing the Source as a whole, moving Lahabrea to call her a parasite and Elidibus to comment on this in their big ARR meeting. Once Zodiark ceases to be a threat, in whatever capacity, let's posit that it is time to allow that aether to flow back into the Lifestream and reinforce the souls once more. How would her Primal directive, "programmed" into her by her summoners, respond to this, particularly if above a certain threshold she would deem it "too much" as reinforced the mass of the souls emerging from it?
Another area of interest for me is whether we have some Lavos/Jenova type being in the setting, responsible for the whole Sound phenomenon, and if so, whence it originated, what happened to it and the question of whether it could return. I'm hoping they go down this route for the Sound, because I like the potential such a being brings with it.
There's also the question of whether this whole story runs deeper than just them being summoned as Primals. Some people have placed significance on the presence of Zodiark's statue on the upper floor of Akademia Anyder, suggesting he may have been worshiped in some capacity before a Primal in his image was conceived. I had chalked it up at the time to a prototype they were considering, as it ran concurrently with them trying to devise a way to deal with the Sound through the summoning of "guardians", but perhaps there's a reason they chose the design... and maybe the same applies to Hydaelyn. In that case, you could have all manner of scenarios, which range from the simplest, i.e. they were mythological entities simply leaned upon for inspiration, to more exotic possibilities like them being Primals summoned in an earlier time (since Amaurot no doubt has a long history), or gods in their own right, given physical form via the Primal summoning. I'm still leaning towards them turning it into a story of Primal summoning gone wrong, writ large, but it's possible that something significant within Amaurotine culture inspired their design.