To make things clear: demons don't serve Lucifer.
In fact, Lucifer has never been royalty, just a rowdy boy rebelling against the forces of goodness. Just the most famous demons, known to have stolen the golden crown of the heavenly king, melted it in the form of thirteen little penises and sold them on earth.
He's adored in hell, but few ever met him, for he has been a fugitive, a criminal within criminals, master at hidding. He's never wanted to be king, and wasn't entitled to.

No, demons answered to the mistress of darkness. All powerful and full of desires, she led armies to the brink of battlefield. She was cunning and fierce. She knew the art of manipulation and would have never been queen if she didn't fool the masterminds of it.

A witch with a demon's crown. A mouse, reigning over lions. A beautiful, strong, evil mouse the kingdom wanted to devour.
She walked the path of respected kings and her people resented her for it. She heard the whispers, saw the glint of poisons, smelled the hatred... but she couldn't be bothered.

She had a mouse of her own, her fiancé, and he was her top priority. Her everything. The human she loved.