I have hemmed my Mothers clothes a very long time. I have a [I call it a hem squirter]. It is a yardstick with chalk holder and a rubber squeezer to blow chalk on the skirt. Put it on the person. make her stand still while you go around her with the squirter putting a chalk line on the skirt. If it is knit, sew hem binding on the cut off skirt and turn it under. Sew very loosley on knit[hand sew]. Because she isn't straight up and down, it never will be straight unless she has it on when you mark it.