letters of rec

Ok so I have a friend that got accepted to SC for this coming fall and is going to rush. I go to a different school but I'm an active member of a sorority that she wants to join, so I don't know where else to ask this question. I know from experience that letters of rec don't do THAT much but it would be nice to help her out any way I can! According to the national website I'm eligible to write a letter but I've heard rumours that the house I'm in only takes letters from USC alums (it's one of the top houses at SC). Just wondering if this was true because I really do think my friend would be an amazing addition! Thanks guys!