how about a papillon 26? or like a previous poster mentioned a speedy 25?
if a smaller bag is her style a pochette is great but it won't really grow with her in terms of being an everyday bag, it would end up being more of an evening bag at some point.
Even though it's designed to be a cosmetic bag, a damier trousse is a great size bag, a bit larger than a pochette but still on the smallish side.
So my suggestions are:
smaller bags: pochette, or damier trousse
larger style bags: speedy 25 or papillon 26