Desiree hadn't meant to harm her.
They had started so carefully - checking in and establishing safewords and trying to have really clear communication. Everyone had always taught Desiree that hypnotized people would ultimately protect themselves. There was no reason to doubt that. Even most studies of behavioral conditioning showed it didn't tend to last that long post-active reinforcement. Extreme conditioning rarely stuck.
So when Laura had gotten more and more into the idea of being utterly annihilated- her personality swept away until all that remained was what Desiree had created- Desiree threw herself into simulating that experience. It might not entirely work- it couldn't!- but it was hot to see how far she could push. She could use all of her experience and knowledge and problem solving abilities to engage in a mutual fantasy-the one she had always had about entirely dominating another person and the one Laura had always had about being entirely controlled. If it got too intense, Laura could always say "stop".
(Ok, they had PLAYED with the idea that Laura couldn't say stop, but Desiree was pretty sure she would actually do it if things got too extreme.)
Laura had given her permission to control EVERYTHING - pain and pleasure, food intake and sleeping, drugs and body modifications and sensory processing. So many possibilities! How could Desiree resist? She pushed mindlessness. Helplessness. Obedience. Dependence.
13 months later, Desiree stood over the shell of a person that was once Laura. She had gotten her wish. She was nothing - no thought in her mind except obedience. Desiree could barely make her eat and sleep, much less leave her on her own for very long. It was like raising a toddler- or someone with brain damage. In fact, she couldn't be sure that Laura DIDN'T have brain damage at this point.
It had stopped being sexy long ago and Laura had become a frustrating, sad obligation. Desiree had tried to reverse the damage but it was like everything in Laura seemed to be fighting her. Attempts to get her old self back only made things worse. Maybe she didn't want that, deep down. Maybe Desiree didn't want it either. Part of her resented how easily Laura was and stayed broken.
Desiree gave up. She couldn't be responsible anymore - not for something that was a genuine mistake. She started planning her escape.