Lizzy Miles was born Elizabeth Anne Peters in one of those isolated country villages that you often read about in books. While she wasn't a princess, she was quite the little dear to behold, and born to an influential family with a great deal of wealth and influence, and thus was helplessly spoiled. She was still too young to really realize that no one there was really her friend - but on some level she knew that when they smiled and bowed they were really just placating her. There was something about the way their faces were too tight, and the way they rolled their eyes before turning to finish an order.
In the hopes of making some friends who were actually friends, Lizzy left the castle one day, assuming that the village people would be just as friendly as those in the castle. They - of course - weren't, and Lizzy soon found herself kidnapped by a man named Anthony Thomas. He was hoping to hold the young girl for ransom against her family.
The experience caused Lizzy to magically mature far faster than she would have normally, and she managed to awaken a hidden power - something that had not been heard of in her kingdom for centuries. If she focuses hard enough, and puts a strong enough order behind it, Lizzy can influence anyone to do anything she wants. It is important that she remain looking at the person, otherwise the effect is weaker, and the harder they fight her, the quicker she gets tired out.
Using her newfound ability, Lizzy managed to escape her captors and run away. She had originally planned on going back to the castle... but changed her mind when she realized that she could have far more fun with her ability if she did not, for returning would cause them to put her in training, etc, and she wasn't interested in that. So she changed her name from Peters to Miles and set out to explore.
One day, when she was hungry, she happened upon a man named Saul Miles sitting and eating his lunch. Smirking, she unleashed her power on him and told him to give it to her instead. He didn't immediately acquiesce - the way the others did - and Lizzy grew angry. She unleashed as much power as she could upon him, insisting that he wanted to do what she wanted him to do. His thoughts rearranged themselves and now she has an - essentially - willing slave.
It's unclear how much of Saul's devotion is because of the spell at this point.