She steers a little closer to him on the sidewalk and lowers her voice. So they won't be overheard. Also to tease him some more.
"I swear my loyalty to you, and the ritual binds it in place. After that—well, it all depends on you. I can argue with you, if you let me; I can do things you asked me not to, or not do things you asked me to, if you let me; I can have a perfectly normal relationship of equals with you, if you let me. But I can't betray you, I can't harm you without your clear consent, I can't disobey your orders in a context where it's clear you mean them to be obeyed. And 'can't betray you' is very broad; I am, essentially, bound to be truly and genuinely loyal to the person you are and not the person I imagine you to be, bound to never deceive myself about what you want or what would be good for you, bound to never interpret your orders antagonistically—that's not the same thing as never looking for loopholes but it's not far off. I have to serve your true and genuine will to the extent I can tell what it is. The spell doesn't affect you directly; all the big magic is on me, you're just, so to speak, holding the leash."
She steers closer still.
"But, say, if you wanted to make me your sex slave? I'd have no choice. If you wanted to make me your slave and not even let me have sex with you? No choice. Make me look up spells for you so you could mind-control me in even more interesting ways? As long as it's what you want, I'd be bound to give it to you."