The Summer Court protects the Inner Gates.
This theory is, of course, baseless, but there's a certain sense to it.
The Winter Court protects reality from the cold oblivion of Outside at the Outer Gates.
The Summer Court protects humanity from the Winter Court.
That doesn't strike me as balance enough (and yeah, I'm the kind of sap who pretends Anakin brought balance by wiping out the Jedi and the Sith, not just by wiping out the Emperor, so precedent is against me, but...). I propose that, unbeknownst to most of Winter (much like Winter's duties aren't known to most of Summer), Summer has more purpose than we've been led to think. And no, I don't mean there's an Insider army that Summer defends reality from militarily.
Behind these hypothetical Inner Gates is the core of all reality. The fiery creative force, emotion, love, what have you, that beats. Summer, then, is the crew watching for meltdown and managing the core radiating into our middle realm. Aurora, then, would have been infected by the core, not Nemesis.
[EDIT: And I think that Core is the World Tree, Yggdrasil, the Tree of the Knowledge of Good And Evil.]
Summer protects humanity from the core melting down, and protects humanity from Winter.
Winter protects reality from the Outside, and protects reality from Summer.
Again, I know, no evidence for it, but I think it at least slots into the cosmic mechanism as we know it.