It all depends on how much she rides. If it's flat I wouldn't go away from a single speed too soon. They're lighter and easier to use. Raleigh has some great bikes that aren't too expensive and you can get a good fit too.
how's this?
http://www.raleighusa.com/bikes/women/retro-1/ , if you can get that in a small enough size it would be really nice. Or are you looking for something a little bit more high performance?