should my little sister join gphi?

Gamma Phi has a pretty poor reputation here to be totally honest, known superficially by most people as one of the "less attractive" or "bottom tier" sororities. However there are a variety of great girls in every sorority(including gamma phi) and she should pick whichever one she fits in best at.

She should give them just as much consideration as the other chapters here on campus. You'd be doing her a disservice by telling her what she should or shouldn't do based on "reputations." She'll figure out where she fits. Just support her either way.

Gamma Phi is considered by most the worst sorority on campus. they have just as much as an opportunity as everyone else to improve their reputation as everyone else, but they don't seem to try at all. If she ends up liking gamma phi the best then 100% she should join, however I will say that joining gamma phi would probably not give her as many positive/fun experience as the others (i.e. Better functions, mixers, philanthropy events etc. ) Yes maybe other fraternities and sororities will go to their events, but they don't have the same enthusiasm/participation that they have at other organizations events. So basically what I'm saying is she should do what she wants, but will probably be better off with someone else.
Also maybe skip filling out the legacy form bc they'll probs keep her forever and might keep her from joining another soroity she likes better. If she really likes gamma phi she will get it 100% no questions asked