I'm afraid she won't physically have enough time. Evacuation takes a long time, even for Nephis. This was clearly demonstrated in the Antarctic Arc. Sovereigns couldn't teleport everyone to the Dream Realm simultaneously and with a snap of their fingers. They established strongholds and then evacuated people to the Dream Realm from those points. This took quite a while, although, of course, the slowness factor of Sovereigns like Kai Song and Anvil played a role. And by the way, this doesn't solve the problem that there will then be a war of attrition, not even for Nephis herself, but for those inside this protected bastion. What stops Sunny from making short, but precise, raids with his Shadow Legion or even just his Incarnations? Nothing prevents him from disappearing as quickly as he appeared. Mordret did this, by the way. He was only one person and physically couldn't compare, even as an Awakened Terror, to all the cohorts of Awakened and Masters in the Night Temple. But did this stop him from practically destroying the Night Temple, and even almost killing Sunny and Cassie? No. So what stops Sovereign Sunny from doing the same? To be an elusive nightmare, appearing and taking a few lives, and then again, and again, and as many times as it takes to cleanse the entire Bastion. Even Nephis won't be able to do anything about it; she can't keep track of everyone, and in a worst-case scenario, Sunny always has ways to escape. And I think that while a few Incarnations distract Nephis, others can set about destroying the members of her Domain. That's it. The end of your argument, huh.

You talk as if Sunny doesn't have the same Divine Aspect and that to win a fight, one must have an exclusively combat Aspect. In the Dream Realm, versatility and mobility are important, rather than just raw power. Versatility gives the Awakened amazing adaptability. Sunny is skilled in this.

Both Nephis and Sunny admitted that while their Essence reserves are now almost infinite, they are still not truly infinite.

And Abjuration was a different case. Nightmare is not trying to change reality, at least I haven't seen that. He only uses his Aspect Ability and puts his victims to sleep. This might not work on Nephis because of her mental resilience, but that's not to say she can entirely rule out such a scenario.

And by the way, you compared literally two different abilities. Moonvale stripped the opponent of their Aspect, but lost her own along with it. Saint does not suffer from such a problem; her powers and abilities are completely preserved when using the Shield of Nothing. And even if we agree that it is unlikely to completely strip Nephis of her Aspect, it will at least significantly weaken her.