The NPC sororities and NPHC sororities do vary chapter by chapter. However, with the NPHC differs in most of their chapters because of the International programmatic targets each of us uphold. Since I do not know what differences are with NPC sororities, I cannot say--some like ZTA do have a "universal philanthropy" with Susan G. Komen. But that is all I know, personally.
The reality is Taurus is that you do well in school, end of discussion. I really am unsure what your qualms are--is it that you want to join an D4 Sorority or not? If you want to join, then first and foremost, if you choose the one that your mother is a member, there are guidelines and rules in place for that. Your mother should be assisting you
fully in that process within limitations.
But, if you do not want to join her Sorority and she might react to it profusely, the whole thing is if you have done all your research like others have stated, then you will know you did the best thing for you and only you. However, remember, parents are just fearful that their children will make adult choices without considering the entirety and gravity of the whole situation. Thereby alienating yourself from her "comforting arms". But, it has happened before and many people do it. So, hey, know yourself.
There is NO directed PLEDGING in any NPHC sorority--it is now called "membership intake process" or "MIP". You make an application to the organization with proof of your grades at an informational (when directed) or Rush (may or may not be invitation only). Rush is NOT the time to decided if you want to become a member--that decision should have been made a long time ago. Rush is when you are asking if you can change your life...
Consider this, just as XYZ is not your material, so is it that you may not be XYZ's material or ABC's material either--legacy or not... You may be PDQ or EFG's material... Or not... Get what I am saying?
Good luck on your education!