This is how I would tackle it. I would cut off about 4 inches to start with. Than measure up from the floor all the way around to where she wants it. Than I would fold up at the hemline at that point and baste with large stitches at the very edge of the hem. Now cut away the rest of the excess leaving about 1/2 inch. Roll the raw edge in and hand stitch. Edge should lay nice and smooth. Just my method, there are others.
