Might depend on several factors in addition to her height and weight. Her body type, and hip placement can also affect which pack fits her best. My wife is 5' 7", 120 lbs, slim and not much curve in the hips. She had a tough time finding just the right pack. She normally wears women's Osprey packs for backpacking, but those backpacking packs just don't offer the support, rigidity, and comfort for heavy pack outs on elk.
We started her off with in Exo 3500, which she said was "okay" (I tried it and loved it) but the when the hip belt was properly centered on her hips, the belt cut into her ribs as well. Then she visited the Kifaru store and spent about an hour with Aaron Snyder trying to find a setup that would fit her body type. The Kifaru felt "decent" but still not quite comfortable with weight in it. After all that fitting, Aaron told her that her body type was just going to make it really tough to find a hunting-style pack that would fit her perfectly. He did recommend that she try on a Stone Glacier though (I really appreciated Aaron's transparency in recommending another company for her).
We went to a hunt expo in Denver and she got to try on the Stone Glacier with about 50lbs in it, and it was an instant, perfect match. Super comfortable, sturdy, and lightweight. We both really appreciated the simplistic design, and she loves that pack after putting on quite a few miles with some good weight in it. I'm so impressed with the Stone Glacier that I'd be tempted to get one myself...that is if I didn't absolutely love my Kifaru!
My suggestion would be to have your wife try on several of the top brands and walk around a bit. The easiest way to do this would be to go to like the Western Hunt Expo in Salt Lake City. It's a great expo, I highly recommend it!
