If I may further expand on what I was saying earlier:
A laptop is a smart investment for a college student for several reasons. First, the mobility means she will be able to take notes on it in class and work on assignments whereever she needs or wants to, as opposed to being limited to her room. Second, a laptop takes up much less space than a desktop, which is an important consideration when away at college. Third, the small size also means she can lock it away (like in a closet) to prevent theft (though you should also invest in a Kensington lock).
Desktop machines always give you more bang for your buck. However, for iTunes, you don't need a very impressive computer. Furthermore, the MacBook and MacBook Pro are nearly identical to the iMac and Mac Mini (they share many of the same internals, like disks and RAM).
One thing that I think currently sets apart the MacBook from all of the other consumer models in Apple's product line (and the MacBook Pro, for that matter) is the fact that it's so easy to upgrade the RAM and the hard drive. Although you can easily upgrade the RAM on an iMac or MacBook Pro, none of Apple's other models, save for the Mac Pro, allow easy removal and installation of a hard drive. In fact, it's impossible to get inside any of the other computers without having to virtually take them apart. Considering the speed with which technology progresses, I like the idea of being able to expand my RAM and storage space without having to completely disassemble my computer.
On a final note, I'd consider the low price of the MacBook (relatively speaking). Computers generally have a useful life of 3-4 years. After about 2 years, they're woefully outpaced by current computers. Given the short useful life, why spend twice as much (or more) on a computer when you can get something that will work well for the same amount of years as the more expensive models? Just my 2 cents...