If she is small (skinny) a lot of the mens packs won't work very well. I have had a hard time getting a pack to fit my wife, she is 5'7" but only about 120lbs, I am going to end up buying a Osprey womens pack for her before this summer. She has worn some of my old packs in the past an had issues transferring the load. I am talking multiple days of backpacking/camping, defiantly get something with an adjustable torso on it. A comfortable pack makes all the difference, a extra $100 might mean the difference in her enjoying the trip and having a miserable trip. IMO