The cheapest she'll ride.
I knew guys with $50 bikes and guys with $2000 bikes in college. Both got ridden the same, both went on the same racks with dozens of bikes, both were left outside in the rain and snow (granted, Northern Michigan is a bit harsher than Florida, and I'd wager far hillier...). The $50 bikes got ridden day in and day out. The $2000 bikes generally did too, people just laughed a lot more about such a nice bike being tortured tested with Wal Mart bikes getting tossed up against it by careless students late to class.
FWIW, old MTB with slick tires can commute well, and are cheap and strong to boot.
Last edited by jefnvk; 04-11-16 at 11:00 PM.