Backpack for skinny girl

Hey everyone. My wife has a Hyperlite 3400 size S. But she keeps getting some really hefty bone bruises on her hips and back from it. And often shoulder pain as well. She had to cut one of the cords on the sternum strap as she couldn't fit it tightly enough for it to actually do anything. And her hip belts don't do much. What backpacks are recommended for smaller people? She's about 168cm. So not short. Just skinny. We live in the canadian Rockies, so prefer something that won't rip in overgrown trails and bushwacking. Is the Kakwa pack better perhaps? Shed prefer to avoid ULA after buying a medium circuit based on her measurements and the websites guide. And it being way too big for her. She doesn't like the brand after they refused to change it.

She has the 55L version. But her pack is barely more full than my 40L hyperlite. She could go a bit more UL. She doesn't have a very heavy pack.