You might look at the Granite Gear Vapor Ki - just pay attention to the rated weight limits, since it sounds like you add weight as you go.

You might also check REI - I think they have some "woman-specific" packs; their stuff appears to be well-designed and reasonably well-built, and they're less expensive since they're a house brand - somewhat.

Don't limit yourself to "women's" packs - also check out some of the packs made for teenagers, and the "men's" packs (probably in size small) - it doesn't matter what the manufacturer calls it, it only matters if it fits YOU.