Ava returned to the castle after sending off the army toward the battlefield. She did not join the main army as she had a different duty. Her duty was to lead a thousand Elven to the border of the Malecia Kingdom. She was tasked to watch over the Malecia Kingdom's movement, and if possible, to represent the Tang Empire to persuade the Malecia Kingdom to surrender.
As for why Ava was chosen for the duty? Because she was an Elven, a former Elven Queen. That way, the Malecia Kingdom would believe the Tang Empire had conquered Gigante Forest. Then it would smooth their operation to force the Malecia Kingdom to submit to them.
Ava entered the main hall and found a maid. "Do you see Lord Tang Shaoyang?" The maid bowed her head. "Lord Tang Shaoyang has not returned to the castle since morning, but I heard he ordered the workers to empty the Royal Training ground." The maid recognized the Elf as one of the Generals, so she told Ava what she knew.