As Mary D points out, you need to decide frame or frameless. If you go with a frame like the popular Granite Gear Packs, be sure to take note of the hip belt. If it is too long, you will not be able to cinch it in far enough to have it lift the weight off your shoulders as it is supposed to. Even if you have an S size pack, you may need an XS belt. The lightest packs have no frames, but if I am out for two weeks, I start to miss a frame to shift the weight. Look at Z-Pack for a frameless. My daughter uses a Dana Design, but they have been bought out by Marmot, but search there or on ebay for older models specifically for women.
PS In fact, I think she has a Deuter women's model.