Borrow a dog crate if you don't have one, or really for me any sort of pen will do - a dog exercise pen, my chick brooder, I've even pulled out a junk tea cart and lay it down on its side and wrapped it with chicken wire. Anything that keeps her from getting back to the nest box and that's safe enough for use throughout the day (and night if possible, otherwise you'll need to manually put her on the roost at night and then re-cage her the next day).
