From a down position place your hand under her chest and lift her up and back to a sit position while saying 'sit'. You lift up as well as back to try and keep her rear legs down while raising her front.
You could try using a clicker and a treat for this and see if she responds. If she already knows sit she should respond after a few tries without the clicker or treat.
Bear, Anna, Molly, Ossie, and The Countess Lisl von Schlaf
An Unhappy German is a Sour Kraut!