Comment Start with screen size (Score 1) 898
It really depends on your budget but the biggest single price issue is screen size - the best deals are for 15.6 screens but if she wants something larger or smaller then the prices for decent machines go up wildly.
Look for a powerful processor with a good GPU that has dedicated RAM, as much non-graphics RAM as you can afford and x64 Windows 7 with good build quality and you should have a machine which will perform well and last a long time.
http://www.cpubenchmark.net/ is really handy for checking on what's good/not for processor and GPU deals
Both Lenovo and Samsung make excellent machines which both look good (which could be important, quite a few of my female friends use Samsung) and have great build quality