Play as carefully as possible and keep moving. If you can’t try to flank Kinessa herself, try and capitalize on any moment she isn’t targeting you. Damage boosting Talents like Blastflower or Scorn are best.
Willo's hitbox is very large and she's slow so you have the advantage if you're able to aim for her wings. If she decides to fly away from her original location, don't track her, predict where the arch will slow down at its peak and shoot there.