I'd suggest a
Priority Ace or a
Priority Classic Plus. These are simple city bikes -- much more efficient and fun to ride than a beach cruiser. They both come with a carbon drive belt instead of a chain, which is a HUGE advantage if the bike will be parked outdoors. No rust, no grease, no worries. The Ace is a single-speed and the Classic Plus has a 3-speed hub (no derailleur to rust or get bent).
Get her a rear rack that she can bungee stuff to, and possibly some Wald folding rear baskets she can put stuff in. And of course, a good U-lock! If you get her a simple, useful bike now, there's a good chance she'll want to use one for the rest of her life.