[tinydancer16]

What kind of "tough" are we talking here? Because if it's a question of a large time commitment being the issue for her then I have to say that it really doesn't get too much easier. Sororities take a lot of time and if she can't cope with it now then it's only going to become more difficult as she progresses in school and her workload increases. I think it would be better for her to decide sooner rather than later, as opposed to getting initiated and then become even more swamped.
I know it's tough because you really like her but ultimately she has to make the best decision for herself and that may mean not being in a sorority -that does not mean that the two of you cannot still be friends, make sure she knows that!