The Soho LOOKS cool, but that's about it. For the price it doesn't seem worth it. I agree that for four miles anything would be fine, but having a nice bike always feel really good . I ride the Trek SU200, although I'd probably go with the SU100 if I had to do it all over again. Just because it has normal brakes and thus most racks fit it, but also because it has a cooler color.

Don't listen to the drop-bar roadies. They'll have your sister staring at the ground most of her ride, rather than traffic.