Just because she sought you out doesn't mean it's right for you to have that kind of power over her. That's not how the law works. She agreed to the original deal under duress with the threat of someone's life over her head. In most places I'd imagine that the dealings of hell and its citizens aren't subject to laws and their consequences that are made by humans, but here, those are the rules we're dealing with.
If you're going to continue using that contract to enforce your power over her, you'll have to break down those intricacies and you should be ready to do it in court because I'm not afraid to take this that far. You're probably used to enforcing all of your deals and contracts through fear, but I'm not afraid of you.