The ACT Lite series is a good pack. Like Mouse said: it has to fit; Deuter can sometimes be a bit finicky. They don't fit me as well as Osprey (I vacillate between an Osprey Atmos 50 AG and Exos 58 - as of today.) I've also used the Deuter ACT Zero 50+15 and ACT Lite 50+10; I preferred the Lite to the Zero, as far as fit - but it never quite hit my sweet spot. Wandering Daisy, on the other hand, had exactly the opposite experience: Osprey's never fit her right, but Deuter was perfect.

Good luck - if she hasn't had a chance to try it on before you ordered it, I hope it fits - the Deuter suspensions tend to be a bit stiffer, and might function better than Osprey at the loads you're thinking she will carry. The +10 is an expansion feature that works especially well in the Deuter designs.