The Doctor raised a brow, staring at the beautiful woman before him with concentrating eyes. He inspected her with simple looks, listening to her fear raising with each subsequent minute that passed where she didn't have her powers, and each realization of just how far this went. Still, he didn't seem to react at first as his mind ran over everything, he then reached out to tap her cheek, "Right! Yes, okay then...perhaps you're sick!"
The Doctor spun with finger in the air, beginning to look around him for something in particular. He then found the little device he used with his magic in order to scan for other magic properties; it served as an all-in-one tool, and it was one of his proudest inventions. It used his magic to find other magic, to sense it; it could also focus his magic, meaning he could use it to fix some things. Flipping it in hand, turned to face her and waved the device at her. Then he frowned, doing it again.
"Oh, that's interesting," Staring at the device, hitting it a few times, before flipping it in hand and slipping it into the inner pocket of his jacket. He moved towards her and grabbed her cheeks, seeing tears beginning to form, reaching up with a thumb to brush at the tears, "You're not sick. It's a thing, not sure what sort of a thing, but a thing nonetheless..."
He stepped back before spinning around for her, "I can't use my magic either. Oh this is brilliant. What could this mean? It could be a spell, but then a spell that stops magic would actually, likely, stop itself. Also would require more than a single Witch, it'd require quite a bit. I wonder if anyone else is suffering from this. They must be, it cannot be coincidence that you and I can't use our powers..."
He looked at her smiling, "Oh won't this be a fun mystery?!"