hard to explain, i dunno, within reason just means within logical means.
Well, logically-speaking she can do basically
anything. Sakura is a devil, and therefore is presumably capable of healing most damage and surviving injuries that would kill a normal person, and there are no limitations on what Caster could have access to, particularly with her magic.
The only limitations on this scene, really, are what I want to see and what you're willing to write. There are
very few things Caster actually
couldn't do to her from an in-story viewpoint.