The Baby is quite a bit smaller than the GS Mini, but both will fit in an overhead bin. The Mini will provide a much better playing experience. Both models look like guitars, so if she's trying to fly under the radar (no pun intended), a Voyage Air would be a better option, IMO. She can put it in a backpack that will not be noticeable to a person "not in the know," and when she breaks it out, she'll have a full-sized guitar (dreadnaught or OM options) with a full-sized neck and full-sized tone.