Take the back of the purse and cut 4" from top to make the zipper opening.
Sew the zipper to the lower edge of the upper piece, turn and topstitch.
Note: for Auntie Bee's purse make the zipper close on the LEFT side because she likes her purse on her RIGHT shoulder and that way it will be facing forward as she wears it.
(I would do it opposite because I carry my purse on my left shoulder.)
Sew binding across the TOP of the back pocket piece.
Lay the lower back pocket piece face down over the zipper with the binding laying on the edge of the lining. This will be sewn to the area right above the zipper. Pin well.
Sew a line of topstitching along both sides of the binding through all layers to attach back zip pocket.
Put a mark on the zipper where the edges of the purse are.
Open zipper and sew lower back panel between marked areas. Topstitch.
The edges are now uneven since we added the zipper so baste the pocket and back pieces together and trim the extra piece off. (I could probably go back and figure out where that stupid extra half inch belongs and adjust the measurements but this way works too.)
Now we've got the front of the purse with inner pockets already sewn and the back of the purse with the zipper pocket done. Next step will be assembly of the purse and the top zipper.