Did she just attack the wrong person? It kind of seems like she may have just attacked the one in the barrier, who maybe was wanting to be brave or whatever and cast yin magic that she secretly knew.
Cause it seems like the one who ran out (kuroko I think it was) ran in a straight line then sensed the yin magic directly behind her and attacked, which would be in the direction of the barrier girl. Oops, some friendly fire maybe.