rather than disagree with another's observation or opinion here, I'll simply draw from my experience with photoshop which is both extensive, and on a professional basis. your video card does matter... as does the speed of your processor and the amount of ram. and on a side note, so does the speed and cache of your drives - both internal as well as external... I work only from hi-spin external disks, leaving my hd or in possibly in yr case an ssd to react only to the needs of the open programs.
the VRAM plays an integral part in photoshop in a number of ways... especially when it comes to plugins. the first and most important aspect of VRAM is how quickly an image refreshes, while performing retouches, such as skin work, cloning and dodging or burning... if your wife uses scripts or actions while performing the above tasks, she will see a marked diff between a 1ghz and 2ghz card. while adobe lags behind slightly if the department of making full use of all our macs can do these days, features such as hyper threading, and extra VRAM will make a visible diff and reduce the time waiting for, redraw, action completions, tasks such as cloning, blurring, canvas rotations, copy and paste from one photo to another such as a vector logo or other type elements... and of course scanned photos - which is where I first got my start using photoshop in '92.
one of the best features that makes use of the additional memory performance of your vcard when working in fashion with photoshop is the option of enabling openGL drawing. this is only possible with a faster vcard and does make use of specific VRAM to aid in advanced features like anti-aliasing and vertical sync.
so zooming, rotations and features like scrolling at high zooms are smooth and without ose horrid jaggies!

I hate those buggers! and of course, the more you can off-load to your vcard the more productive your processor will be.
do you NEED the extra VRAM or .3 ghz? simply, no. does it make a difference to a professional spending 8+ hrs a day in and out of photoshop and maybe bridge or aperture or lightroom etc... yes, it it does.
I teach photography, to both students of film and the digital age... and one of the first thing I teach is to get the most you can for your money. that is true both when buying a camera these days and the computer you're going to use to process your work - whether it be scanning and retouching film shots or simply importing digital shots straight from your camera.