First and foremost, ensure that laptop meets Photoshop minimum system requirements. Display will be particularly important. Photoshop minimum "1024x768 display (1280x800 recommended) with 16-bit color and 256MB (512MB recommended) of VRAM."
Two other important specs: 64-bit windows OS and a separate graphics card for GPU support (OpenGL 2.0–capable system).
General recommendations will include minimum 4GB RAM with as much more as is reasonable considering cost and use environment (weight, battery charge life). Similar for processors -- multicore -- depending on work she'll be doing - fast processors may be important (for some 3D and processing large camera raw files, should she be planning to do these).
Review "How to tune Photoshop CS6 for peak performance" <http://blogs.adobe.com/crawlspace/2012/10/how-to-tune-photoshop-cs6-for-peak-performance.h tml>.
Consider also what she may want to do with the laptop over the next three years or so. Perhaps configure more than needed for today with an eye to greater system resource demands in the next year or two.
She's angling for a Dell Alienware gaming computer, with
- 3rd Generation Intel® Core™ i7-3630QM (6MB Cache, up to 3.4GHz w/ Turbo Boost 2.0)
- Windows® 7 Home Premium, 64bit
- 14.0" High Def+ (900p/1600x900) with WLED backlight
- 8GB2 Dual Channel DDR3 SDRAM at 1600MHz
- 750GB 7,200 RPM SATA + 32GB mSATA Caching SSD
- Slot Load Dual Layer DVD Burner (DVD+/-RW)
- 2 GB GDDR5 NVIDIA® GeForce® GT 650M with Optimus™
...so, is this crazy-too-much, or reasonable for a 3-4 year projected lifespan?
Looks like a good high-end set of specs that should go nicely beyond immediate needs. HDD 7200 rpm + SSD a good choice, I7 3630QM good for now & into 3-4 year time. She'll want to apply her systems skills to manage what goes on the 32GB SSD and what to redirect to the HDD (one suggestion: be sure that Bridge cache, and maybe camera raw cache, are assigned to the HDD). It would be good for her to closely look at the 1600x900 px display -- packing lot of pixels into a small 14" space for some graphics work (I'd have preferred 15.6"), but young eyes can handle that. The 2GB GeForce® GT 650M may be more than Photoshop needs, perhaps useful for video and games (assuming they'll be on the system too).
Any way to upgrade the hard drive setup to pure SSD? Caching SSD hard drive combinations are known to be problematic. Spending extra money for a premium SSD solution (e.g., an OCZ Vertex 4 or Vector 512 GB SSD) would both improve performance and make it less likely she will lose data. Laptop hard drives fail more often than desktop hard drives.