Laptop for a college student?

I want to buy my sister a laptop since she's starting college in about a month.
Looks are a big concern here. I want her to have a laptop that isn't too bulky and looks "stylish".
In terms of specs, something with an i5 would be preferred, but would be willing to bump down to an i3. screen size should be between 13 and 16 inches.
Looking to spend between $500 and $600 but can go up to $700 if it's a slick deal.
Also, it has to be one that will last her a couple of years.
Thank You.