In the conditions they were in, the large reach of Soulsong was a disadvantage rather than an advantage. While it was no ordinary blade, Kiri would fare better fighting without it, for now. After all, in hand-to-hand combat, she had more resources at her disposal. She could use her wings to deflect attacks, as well as her tail. Her tail could also be used to attack with. While Gen may be extremely skilled, he was still human, and humans only have so much they can use.
As she got closer, Kiri swung with her tail to strike first, since it had longer reach than her arms.