Belle was trap in both physical and mental way, the pendulum she can't stop looking at is giving free way for you to control her like a slave, and all you have to do was tricking her into following you and not be interrupted by her brother.

You begin to put suggestions in her brain to be used on your favor and have control over her without the use of the pendulum, for such a naive girl her body is completely gorgeous.

— Such... Good... Feeling of being... Yours... I want to be... Yours... Don't stop... She says in a dreamy trance as her mind keep recieving suggestions.