You really need to fit the pack to the specific person, the specific gear and the total package (specific gear and specific person together). That's what I mean when I say the most important items are fit, fit and fit. Box up the gear she will carry and take it with you. I don't want to hurt any feelings, but IMHO "some weight" won't do the job.

Packs that I would look at for me should my current pack fall apart (no danger of that happening yet) are the Elemental Horizons Kalais and the ULA Ohm 2 or Circuit (the last is heavier than I'd like). I frankly have never found a pack at REI that I would even consider, but that's me. I can't even find a daypack that fits there (nearly all their daypacks are now unisex and therefore way too big for my short torso). And I won't consider a pack that weighs much more than 2 lbs. YMMV, of course!

If you insist on REI, don't eliminate Deuter from the mix. Or Osprey--not everyone has hips like mine (I hope not, anyway)! Try to make an appointment for an uncrowded hour when their most experienced pack fitter is there. If there are any specialty shops (backpacking or mountaineering type) in your area, you'll probably get better service.