Here is the full list of all 13 Dark Maidens achievements.
Defeat Abigale on Normal
Defeat Abigale on Hard or Higher
Defeat Trina on Normal
Defeat Trina on Hard or Higher
Defeat Slan on Normal
Defeat Slan on Hard or Higher
Defeat Gila on Normal
Defeat Gila on Hard or Higher
Complete the Game on Any Difficulty
Defeat 150 Enemies on Normal
Defeat 300 Enemies on Normal
Defeat 150 Enemies on Hard or Higher
Defeat 300 Enemies on Hard or Higher