SINNER: Sacrifice for Redemption

In order to obtain this achievement you must parry three of Chanel’s attacks despite it stating ‘countering’

You will need to time your block (LB) at the correct moment to parry an attack - doing so will knock Chanel back and allow you an opportunity to counter her attack.

Cower Before Me adds that dodging and retaliating shortly after can also be classed as a counter to Chanel's attack and unlocked the achievement.