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
I have a TZ5000 which is super adjustable for sale. I'm looking for $280tyd. I'm just trying to make back what I bought it for since I upgraded. It's in great shape only trained a handful of times in it. Not sure if it'd fit or not you could look into it. Feel free to PM me if your interested.
I have a Mystery ranch nice frame and 2500 cubic inch pack. works great for upto 3 days for me. I am about 5'7 and 130lbs and it is super comfortable and fits great. I'm looking to sell it, feel free to PM me. She might need a bigger yoke than me but Mystery Ranch is selling them for pretty cheap right now if you call them.