Use area effect skills that do not require a target, or drink a shadow potion until the Blind spell wears off.
Josephine summons a death knight first, then casts a spell on it, then casts Blind... in that order, without skipping any steps. Similar to what Carrie suggested, if you interrupt her spell (maybe try Flash Attack, if you have it), she will keep trying to complete the summoning and never move on to casting Blind. As a warrior, with a sword and Stun, I just ran up and whacked her right after the conversation ended, and didn't loose a hit point.
