Yep, it fits, but lugging around a 15.4" notebook along with books isn't fun (around 6 lbs). You want to cut back on weight wherever possible, especially when mobile, and especially when you are of a sex with lower upper body strength- possibly walking miles every week on campus to and from class.
I did the whole college + laptops + books + backpack thing. Smaller is better, so long as your eyes are comfortable with the screen size, and your hands fit on the keyboard. 12.1" to 14.1" is the best size for school. I had the choice between a 15.4" and a 14.1", and even though the 14.1" was slower and older than my 15.4", it was my choice since it was more convenient. If I had a 12.1" back then, there's no doubt I would choose it.
It's a lot easier to pull out a 12.1" notebook with one hand in a hurry than it is to pull out a 15.4". It also takes up less desk space, which in many colleges is simply long tables that you share with other students (either that or your lap if you are in a large lecture hall with theater seats).
I probably should also mention that the smaller the screen, the less likely it will suffer pressure damage from books. If she gets a larger laptop, remind her to face the top of the laptop away from the book compartment on her backpack, that way the pressure from the books edges will be applied to the bottom of the notebook.
12.1" are usually very expensive. 13.3" are also expensive, and a bit more uncommon. 14.1" are common, but generally more expensive than the mainstream budget notebook ,which is 15.4". I say 14.1" max for college, especially for someone with a smaller build.
