In reply to Sherlock:
I think you need to narrow down the search a bit
For summer hillwalking then about 20l should be fine, 30 tops. At that sort of volume the hip belt isn't load bearing, so doesn't need to be padded (unlike shoulder straps) but personally I find it useful to have some external storage that can be reached without taking the pack off, so hip belt storage is pretty handy. Back padding not vital as will be full of clothes anyway probably, but some sort of padded stiffening sheet makes sense for the minimal extra weight. About 5-600g is plenty for a bag of this size. Clean lines preferable over a multitude of zips and straps.
Some companies seem to think 1kg is fine for a daypack - I think that's crazy talk. Does she need to carry poles, ice axe, or crampons at all?
Personally I dislike side pockets, but a good top pocket that swallows handy things easily is useful.
The Blue Ice Warthog 28 often pops up half price on sport pursuit, and I think would be a good choice.
b