Deal with her mind

"You-you can't...do this..." Keyleth gets out between moaning like a bitch in heat, which she technically is.

You sigh. Being omnipotent removes the challenge of life, but you still sometimes wish people would get it through their thick heads, that their morality did not rule your existence.

You reach up and grab one tit, twisting and tugging roughly and forcing the whore into a new a series of wanton movements. With your other hand, you scrape one fingernail across the edge of that swollen, ridiculously sensitive pussy, sending her into orgasm after orgasm. A bimbo who gets exhausted is no fun, so you increase her endurance with a thought, allowing her sessions of entertainment to go on for days if need be.

Then with the Reality Marble, you reach out toward that beautiful mind of hers. She is hardly intelligent, not compared to an eldritch being such as yourself, who has swum through the sea of universes and gazed at the terminus of eternity. Still, she is wiser than most humanoids on this pitiful planet. You let her keep her wisdom. You want her to know that it is wrong to spend hours masturbating for the amusement of an abusive master. You want her to know it is wrong to humiliate herself in front of others.

And you want her to be incapable of helping herself.

You let her keep her wisdom but strip away what little charisma she had built up, taking away whatever purchase she had to once being a leader. You replace her slightly smoky, good-natured voice with the high pitch screech of vapid whore, unable to use words more than three syllables long. You trap her rebellious soul and magnificent mind within the shell of an idiotic slut.

Perhaps, when she learns to behave, you'll allow her to express herself with slightly more dignity.