Perhaps what makes this scene so heart-breaking is the fact that you have this moment of great jubilation. The Air Nation has gained a new master and is starting the era anew. It truly is a moment to be happy, and here you have Korra just not in it. She helped created this but by the look on her face, it doesn’t even appear as though she even there. Her expression is completely blank and void of life. Absolutely empty.
She has the look of a soldier whose returned from war but hasn’t truly left the battlefield.