#1 question she has to ask to herself is what is she planning to do with the macbook. If she planning to do video editing or other high cpu stuff, I would get the Macbook Pro with at least 256GB of hard drive space. If she likes to do a bit of gaming that requires a good video card, get the macbook pro as well.
However, if she going to use it to do school work (reports, etc), Facebook, email, etc, I would go with the macbook air. Also, if she planning to do a lot of travelling, go with the macbook air.
Lastly, If she can wait for a few months, hopefully Apple will release newer macbook airs with the broadwell processors. They are designed for laptops like the macbook air.