The only way to get this achievement is with a 180-degree sword swing. Klarinetta will swing her sword 180 degrees when you press the diagonal direction that is opposite of its current position. For example, if the sword is facing up+left and you press down+right, she will do a 180-degree sword swing.
Keep in mind that she will always swing her sword clockwise when doing this.
EDIT: You can choose whether to swing clockwise or counter-clockwise now! Pressing the opposite diagonal as the sword's current position will swing clockwise, and pressing the same diagonal as the sword's current position will swing counter-clockwise.
The easiest way to unlock this achievement is killing the conga line zombies during a King Conga battle.