Women's packs tend to be narrower and may fit better...worth a try. 

For example the Gregory Maven 55  S/M  supposedly fits a torso of 16- 20 inches and a waist of 27-46 inches

https://www.rei.com/product/159409/gregory-maven-55-pack-womens

and the Gregory Diva 60  M  supposedly fits a torso 18-20 and a waist of 28 - 48 inches. 

https://www.rei.com/product/125757/gregory-deva-60-pack-womens

The smaller torso sizes of these bags fit slightly smaller waists and on the deva the waist bands can be switched out so you can probably get a M bag with a small or extra small hipbelt.