Inside his heart, Ainz rejoiced. He had not lied to Narberal. Ainz’ current state as a Perfect Warrior meant that he could not use magic. Thus, using Narberal to relay messages from Demiurge was only logical. But there was another reason, one that he could not say out loud.
In order to better pretend that he had already seen through Demiurge's plans, and not let Albedo and Demiurge suspect anything, he had to minimize contact with them.
If he assigned Narberal to do it, it would be like playing a game of telephone, and some of the information might end up distorted. However, he would rather take that gamble than risk damaging his image as the supreme ruler of the Great Underground Tomb of Nazarick.
Ainz slowly made his way back to Evileye.
While Narberal was talking to Demiurge, it would be up to him to draw her attention.
"Really now... it'd be good if we could somehow get through this. Speaking of which, I wonder what the face of a child with such power looks like under the mask...”