Taking in those side seams with the faced armholes and pockets would give you very bulky seams as well as making the fit narrower.
I would put vertical darts on both front and back.
Have her put it on wrong side out, and pinch in at her narrowest part, slightly above the natural waist, and use safety pins to position that. You'll have two in the front and two in the back. When you achieve a flattering fit, lay the dress out on a flat surface and lightly pencil in your darts ending in a point under the bust, and ending in a point above the hips. I have done this for myself. She will still need to use a tank top or a tee shirt.