@mods: I think this thread should be moved to the Wilderness and Survival sub-forum.
@keepitsteady: The Mora Clipper looks like a fine choice. If you find that caring for carbon steel in a wet environment becomes a problem for you, another alternative would be the Buck Bucklite Max Large, which has Buck's great 420HC steel and a 4" drop point blade. Can be found with a nice safety orange handle too.
FWIW, while I find it comforting to have a fixed blade in my pack, I end up using a folding knife with 3" - 3.5" blade. The Buck Ecolite 112 or 110 are solid choices (if you prefer stainless), as is the Opinel #9 or #10 (if you prefer carbon). I find that sheath knives interfere with the hip belt of my pack, and I strongly to prefer to have a knife on me at all times. So, I carry a folder in a front pocket. Light weight is a huge plus, hence the recommendation of the Ecolite or Opinel. These knives handle almost anything I've ever encountered in the 30 years of backpacking, climbing, ski and bike touring I've done. Almost...
I find there are other tools needed on the trail. Scissors are needed for bandage prep (it's when, not if) and small pliers, drivers and such are useful for driving needles through heavy materials to repair a busted pack or tent or repairing a failed stove in the field. I carry a very small key ring sized Leatherman in my pack for this. Just enough. The EDC sized ones are reasonable to carry too, but I cant recommend the full sized ones if you already have a real knife. Just too much weight for not that much extra functionality.
Two things worth mentioning as you and her plan and prepare (a big part of the fun!!)...
1) When talking about such things on forums, I find it useful to be aware that there are several different traditions or schools of thought about backpacking and wilderness travel. There is the classic backpacking/mountain climbing point of view. There is the hunting/fishing/pack animal point of view. There is the primitive survivalist/bushcrafting point of view. And, increasingly, there is the military/tactical point of view. Each is legitimate. And you'll find forums with biases one way or another. I mention this because the feedback and guidance you'll get will tend to go in very different directions depending on the tradition. There's no one right answer and the right answers will conflict.
2) While I hunt and am very comfortable with that tradition, I have the most experience as a backpacker, climber and ski tourer, so I'll speak out of that tradition for a moment. Many people hike great distances like the Pacific Crest Trail or the Appalachian Trail carrying nothing in way of a knife than a key ring sized Victorinox Classic SAK. It's not at all unreasonable if you fully embrace ultra light hiking techniques (rely on a stove for heat) and leave no trace ethics (avoid cutting vegetation in high use areas). As noted above, I'm more comfortable with a bit more than that but the point here is that you should feel free to carry as much or as little knife with you. It really depends on your approach, what techniques you use and, in the end, what makes you happiest.
To this end, here are some of the books I've found to be the most helpful in learning backpacking skills: "The Complete Walker" by Colin Fletcher, "The Backpacker's Handbook" by Chris Townsend, "Backpacking: One Step at a Time" by Harvey Manning (dated, but still very relevant and a real classic).
Have a great time!
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