Well just to confuse matters more, im a freelance graphic designer and video editor and i do 75% of my work on my laptop, I've just gone from an ASUS gaming machine to a Dell 16" XPS laptop and freaking love it. I will never by an ASUS again. Seemingly great value for money re: specs, but soo unreliable and fragile.
hackR. I studied graphic design at university in the US and Australia. Go with the mac. Its the industry standard for graphic design (as it is for video production and photograph - though not web design) and if she gets a windows laptop her professors will tell her she has the wrong platform. This is because 5 years ago mac was a bucket load more stable than pc, these days though there is basically no difference (which is why i use the slightly more cost effective PC). That being said though design professors (i studied in NY) are generally stuck in their ways (i had to do typography classes by cutting and pasteing by hand individual letters to make up entire paragraphs!) and like to loudly tell students their opinions as if they are solid facts. So what you really dont want is to convice her to go with a PC, drop $4k inc software, and then have her professor tell her to buy a mac!