Rachel gave Sonya a 'you caught me' look when she asked about the soul stealing bit. "It's something that I can relate to. Not in the same way as what you are talking about. But... just not being in complete control of my own actions."
She was talking about the demon marks. One she had gotten rid of but she still wore the one. Plus, she had an unclaimed vampire bite where basically any vamp could put her under their thrall. That's if that's how things worked here. She wasn't even sure about that part.