Alright, without knowing anything more about what she plays, here's my suggestion.
Core i7-2700K $370 (same speed and Turbo as fastest socket 2011 CPUs)
2x8GB 1.5v DDR3-1600 $130 (nice to see price come down on 8GB sticks)
Asus Maximus IV Gene-Z Gen3 $190 (one of the best boards on market, and it is mATX and affordable)
random aftermarket top-down CPU cooler $50 or so (anything better than stock, drop fan speed low)
1GHz Radeon 7970 $600 (fastest single card, no SLI/CFX profile madness or micro stutter)
550W modular 80Plus Platinum PSU $160 (oh yeah, Platinum)
Lian Li mATX case $100 (small and attractive, like a woman I know)
Blu-Ray burner $80 (why not?)
3TB data drive $210 (got data? use for backups?)
256GB SSD Windows/applications drive $330 (fast Marvell controller, 5 year warranty)
512GB SSD games drive $650 (fast Marvell controller, 5 year warranty)
Windows 7 Ultimate 64-bit $190 (because Home Premium limited to 16GB, leaves room for upgrading RAM)
=$3060
This gives you some leeway in pricing/sourcing plus some profit. The purpose of the parts choices listed after the part.
The overall philosophy of the build is to be small and attractive, with reasonably low noise and great performance/Watt. With all the SSD space, only backups and data will not reside on SSD, so everything should be super snappy.
This is not a "how much gaming performance can I get" build (for that you will need to overclock CPU at least). However, it is a monster in its own right. Can easily spec twin Radeon 6950 in SLI with higher wattage PSU and normal ATX case/mobo, but that's not the point of this build.
It also avoids possible pitfalls by not doing RAID or SLI/CFX and choosing the more reliable Marvell controller for the SSDs instead of the popular Sandforce.
Possible changes: If data drive not needed, drop the HDD. If Blu-Ray not needed, step down to $20 DVD writer. If not that many games will be installed at one time, drop the 256GB SSD and run everything off one 512GB SSD. Can probably knock $80 off the cost by going with an FSP Aurum 80Plus Gold PSU instead of an 80Plus Platinum. Since not overclocking, can easily go with a full featured ASRock Z68 Pro3-M board and save $70. Alternately, bite the bullet and overclock that biatch! Heck, with Sandy Bridge most people would be confident enough to overclock for customer's systems. Heck, there are a few boutique builders who offer AND GUARANTEE the 2700K at 5GHz overclocks! I think 4-4.5GHz is a shoe-in for years of reliable operation. If no overclocking and noise really not an issue then can save $50 (give or take) and just use stock cooler since it really is sufficient for stock clocks. Here is the build taking these suggestions into consideration:
Core i7-2700K $370
2x8GB 1.5v DDR3-1600 $130
ASRock Z68 Pro3-M $120
1GHz Radeon 7970 $600
cheaper 80Plus Gold PSU $80
Lian Li mATX case $100
DVD writer $20
512GB SSD $650 (fast Marvell controller, 5 year warranty)
Windows 7 Ultimate 64-bit $190 (because Home Premium limited to 16GB, leaves room for upgrading RAM)
=$2260
Of course just add $70 for the better motherboard and $50+/- for aftermarket CPU cooler to OC the CPU.