You don't say what transmission she wants. No point in getting a Metro/Swift/etc unless she's willing to drive a manual. The automatics were ancient 3-speeds (with no lock-up) that return horrible fuel economy.
Personally: I'd say there's some merit to the idea of sticking with what you know - there are efficient options in Hondas in that price range.
(Sticking with what you know is also Frank's advice, though he wants you to stick with what
he knows.
)
Maybe we need a stickified thread - this kind of question comes up a lot... "what used car should I get that's efficient"