There are some women specific rucksacks, and it's certainly worth trying them.
Ellis Brigham in Fort William steered me towards a Lowe Alpine airzone 45/55 which they seemed to think was woman friendly if not woman specific, which has served me well for many years/multiday walks.
But really the only thing to do is try a lot on, and walk round the shop for 10 minutes or so with a bit of weight in them and see which is the most comfortable. I tend to do b&bs and hostels and don't carry camping stuff, and a lot of people manage with a 35l sack for that kind of thing, as I have for 2-3 day walks. They must be better at packing than me. It's not that I take more stuff, I find a rucksack which isn't stuffed to bursting is more comfortable, and on multiday walks you sometimes end up needing more food space.