I would look at Jamis bikes. I am 5' tall and just bought a 13" Durango 2. It's probably too heavy for your gf, but I didn't have quite the budget you did!

Jamis makes a LOT of mtbs in 13" size which I find fits me great! I also have a Jamis road bike and I gotta hand it to them, they know how to make small bikes for small riders. Jenson USA has a lot of last years models on sale.

http://www.jensonusa.com/store/sub/1...&pricemax=5000

I live local to them so I was able to test ride a bike. They have awesome customer service.

(nope, I do not work for either Jamis or Jenson, just a happy customer!)