The G650GS would probably suit her. It is a single and is a little lower than the F650/700GS or F800GS without a lower seat or having it lowered.
I'm 5'5" and have the F650GS with just the lowered seat and can flat foot it at stop lights. The GSpot forum would be a better spot to have posted this.
ADVMax: BMW's do not break down - they fail to proceed.