Actually, the Deuter Fox 30 does have a good frame and excellent suspension. I tried several different packs on my grandson and he found the Deuter by far the most comfortable. At age 11 he carried total pack weight of 15 lbs. last summer with no complaints. I was the one complaining because he was out-hiking me, which will obviously be a regular complaint from now on!
You can always whack off some of the unnecessary gewgaws and get rid of about half a pound. One problem here is that the kid may object violently, as did my grandson, to having anything removed! You may not want to, either, if you want to sell the pack when it's outgrown (not so much of an issue here because my grandson has two younger siblings to inherit the Deuter Fox).
I'd either take your girl to a good backpacking store to be fitted or else order 2-3 packs at once, try them on and send back the ones not chosen. If you're near an REI you can have them sent to the store and get help trying them on there. (REI has its own brand of children's pack you might want to try, too.) Pack fit is almost as individual as shoe fit, and IMHO for children fit is even more important than for adults--especially if we want them to love backpacking!
I personally don't like frameless packs for kids unless the total load is less than 10% of the child's normal body weight. However, MLD has one of their packs (I think the Prophet) in extra small size and one of our BPL members recently developed a couple of really light children's packs: http://www.backpackinglight.com/cgi-bin/backpackinglight/xdpy/forum_thread/50198/index.html?skip_to_post=425524#425524
The problem is what to get my grandson now that he's almost 12 and outgrowing the Deuter Fox. It was adjusted to its maximum last summer. The next size up in Deuter is almost 4 lbs., which is far too heavy. I'm hoping he'll be able to wear a size small in an adult lightweight framed pack, such as a ULA Circuit or the Elemental Horizons Aquilo with the extra stays, or the new smaller pack that Elemental Horizons is developing. We are going to wait until spring and see what size he is then!