To her credit, Willow only flinched ever so slightly. She could feel her magic starting to drain away - depleted without any means of rebuilding itself other than the old fashioned way. Which, really, was going to take too long to be of any more use to her here. Fortunately, though, Willow had been fighting demons for a good while before she'd even discovered she was a witch. So she did have a few tricks up her sleeve and one heck of a quick-thinking brain to rely on to (hopefully) get her out of this mess alive.
Green eyes narrowed a bit as she announced, "Right back at you... jerk!" Then she flung the bottle of holy water in his face.