Putting her in a circle to fight the DO doesn't really fit her role

Neither does it fit Nynaeve's role really (healing). And putting her in a crucial circle with Rand has already happened. This would be redundant.

What would such a circle accomplish? Being a great killer is not the answer for the DO. The failure of Dark-Rand is proof to that. And Shadar Logoth for that matter.

Being a great healer is not the answer either. Throughout the series we witness the futility of healers against the might of the Shadow. Rand's wounds remain unhealed, his madness beyond the capabilities of Nynaeve, the taint on saidin managed only after 3000 years of dilution, the use of another taint and the prop of the no longer existing mightiest saangarels in the world. The very failure of the pacifist second agers is proof enough of that.

What's needed are Dreamers. The importance of Teleranriod is brought to our attention again and again. It's the only thing beside the Creator and the DO that has such a central place in the Pattern. All the early fights Rand goes through happen in Teleranriod. And the fight between the Dragon and the Shadow is at its center one of dreams even if we're never told explicitly that Rand is a Dreamer. It's about hope and belief and vision of what the world should be.

Rand, Egwene and Mierin are the three central dreamers in this world. It's their moment to shine.