The other responses above certainly convey the tone of concern over offering suggestions, since no one really knows your girl friend. I think, however, there are probably some "constants" that apply here when buying for the distaff member: buy something that is attractive to look at, takes up relatively little space, is reliable, and is easy to use. If you can combine those characteristics with decent sound, you'll probably have a winner. Many women find complex audio systems to be "user UN-friendly", and if your girlfriend does not find the system fairly intuitive to use, your best efforts will not be appreciated. (I also used to be an audio salesman, and take my word for it when I say that most women have very different objectives for an audio system than men.)
In this situation, I would NOT suggest buying used gear. It may not convey the message you want, and you'll have no warranty in the event something fails.
I recently put together several small systems for women who are friends of my wife, and the system that best met all of the criteria I mentioned above was built around the TEAC Reference components. This line has small, very nice looking units that also have pretty decent sound quality. There are two integrated amps to choose from (30 wpc, and 50 wpc), a tuner, and a CD player. All have gold-anodized finishes, and are easy to use. (An option to the CD player is to buy a decent DVD/CD player, which provides two functions for the price of one.)
For speakers, you've got some good, low-priced options. You might start by contacting AudioAdvisor to see what they have on sale -- they've recently had several good yet compact speakers on sale for around $200-250. The new Mission M71 speakers also got a superb review in TAS or Stereophile. Another option is one of low-priced speakers form PSB or Paradigm.
For a starter system, then, keep it simple, attractive, and easy to use, and you're 90% of the way home. The suggestions I've just listed will also provide pretty decent sound, and if your girlfriend likes what she hears, you can then help her upgrade the system over time.