Smiley said it pretty well.
Just to add to it, I'll try to categorize some of the schools for you quantitatively (I'm an econ major, everything is better for me in numbers

)
FSU, UCF and UF have very large, competitive rushes with quotas in the upper forties to lower sixties range.
USF, UNF, UMiami and Stetson have smaller, less formal rush processes. Their quotas are all over the board, but from what I've been told (someone please please please correct me if I'm misinformed) they do not exceed the forties.
FCGU, Rollins, FIU, FAU and Jacksonville University are even smaller schools as a whole with naturally smaller greek systems. For example, FCGU has only 3 sororities.
That said, I've seen juniors receive bids at UF, so its not impossible per say, but can be difficult at the school where there are 900 freshman rushing. It helps to have friends currently in the school's greek system.
I hope your friend decides to give it a try!