The elders knew about the gods' non-intervention agreement, but they didn't know that Eirin and Canan were one. Eirin didn't trust any of them to share such an important, intimate secret, so they were oblivious to her unique status.
To the elders of the Order of Magic, Canan was the Emperor and God of the Makima Empire, while Eirin was his younger sister and demigoddess, as well as the founder of the Order of Magic.
It made no sense to them that she should not participate in the war, as the non-intervention agreement was not supposed to stop her. They were assuming she would be busy fighting Setlan and the Fae alliance's attempt to retake their territories from the Makima empire, but she has yet to be seen on the battlefield.
"A couple of masters of magic should be enough to keep an eye on him, though not enough to defeat him in battle. We could also use energy signature tracking spells to ensure he can't run away." Eirin suggested.