good lightweight womens pack

Me and my ULA Ohm meet those criteria.

I've been pretty happy with that pack.

If you're looking for something with a frame (the Ohm is frameless), the Klymit Motion 60 is what I'm using these days. It's not a "women's pack" per se, but in the S/M size it fits my very short torso well, and it has "S" shoulder straps (better for most women). It weighs about 2.5 lbs.

The Ohm is not frameless. Not a typical frame, but it does have a rod to provide structure.

yes, the Ohm has two rods, connected by a more flexible material in arc at the top. Weight transfer to hips seems pretty effective.

Just did the JMT with a brand new ULA circuit and loved it. Amazing load shifting capacity for the weight. With 25-30 pounds it felt better than my old luxury arcteryx; with under 25 it was even better. I am 5'5" with tiny shoulders, and have size small with s-straps. Could try the Catalyst if you need more space.

Osprey makes some nice backpacks. I have one (Aura 65) that's a little under 4lbs but if I have to carry heavy stuff it feels comfortable. I can also take the lid part off to reduce some of the weight.

I should add that Osprey has some lighter packs than the Aura 65.

I'm about your daughter's size and like both the ULA Circuit and the Z-packs Arc Blast. The Circuit is the most comfortable pack I've ever had and is bulletproof, the Arc Blast is expensive, extremely lightweight, and is waterproof (if you are careful with it).

My daughter is 5'6", slender, and likes the ULA Ohm 2.0 Size Small with S curve straps.