Based on what Thorndyke says, while Ouroboros seems to be opposed to the Reset, it were their actions which made it increasingly likely (the removal of the Sept-Terrions).

I do frankly not see how anyone is going to stop the next attempt without Ouroboros' aid, which explains why the ASO crew was allowed an audience with the Grandmaster (ruling in the Anguis is usually the job of the First).

The Grandmaster can not merely impede Sept-Terrions with the Divergent Laws (which also means the shackles/barrier do not stop her) but she has a Sept-Terrion (the Aureole) and an Aion to interface with it in real space.

She also said that she needs Novartis' support.

So the most likely course of action would be to send the Aion to outer space after linking it with the Aureole, which probably allows them to trap Laegjarn in a space bubble with no ability to interact with the rest of the world. This also doesn't require interference by the Grandmaster.

If this plan succeeds the Grandmaster would obtain the Sept-Terrion of Time.

No on to the name Ouroboros and the snake biting its own tail. What if the Grandmasters aim is a rewind, just not the usual one which doesn't go further than S.0?

If the Grandmaster made it past that year she could prevent both the Great Collapse and the creation of the Septian Church.

Given that Laegjarn also seems to take the souls of the deleted people, things like Orpheus and the guiding Flame make sense, too, because the Grandmaster maybe intends to bring everybody with her to that age.

The question is the motivation, and it could eb that back then something happened to the Beyond, too. (McBurn suggests some ill fate befell it.) Maybe there was a war between Zemuria and the rest, and McBurn supports her because she wants to unwind the mutual doom.