Demons Are a Girl's Best Friend

A story about a demon with no feelings and a girl with too many.
Having lost it all, Sylvie summons an ancient demon to release her from her pain. Little did she know, however, demons are not as omnipotent as she thought. In fact, they have three rules they have to abide by:
1 - They cannot take or resurrect lives
2 - They cannot influence hearts
And .... ?