If you're willing to spend a little more, you can upgrade to pretty extreme comp that will be time resistant so that she/you can play all upcoming games.
ME has a bundle of i7 and z68 mobo that is pretty damn killer for the price.
Intel Core
I would have gotten this if I didn't already have the exact same setup.
Then the ram you need here (you could get 1 but 2 to max out at 64bit win 7).
Kingston HyperX Genesis 4GB DDR3-1600MHz CL9 DIMM at Memory Express
Case and PSU to whatever you want. Then get a used graphics cards on CL or RS for cheap and you'll be done.
So here you'll have
CPU - i7 2700k
Mobo - Asus P8Z68-V Pro / Gen 3 Motherboard
Ram - Kingston 4GBs 1600 mhz (or 8GBs if you get 2)
Total cost: 509.98 + tax = 571.18 - 20.00 (rebate) = $551.18
For under 600 dollars, that's a pretty killer setup. You could add the other 4gbs of ram for 19.99 and the total goes to $593.57 with taxes (573.57 with rebate).
Missing
PSU
Case
Graphics