I am a Graphics Art Graduate but am currently working in an IT department. My company uses Apples for all their graphic design needs and are very happy with them. If your grandaughter likes using an Apple, buy her an Apple. If she likes PCs, I recommend buying a Dell Latitude D810 with the upgraded WXGA screen. This has a larger screen area and would be better for Graphic Design. Its what I use for my side business.
I fix Dells and I fix IBMs all day long. Dell has a better product and a better warranty right now. (subject to change)