letters of rec?

hey everyone! I will be rushing in the fall and wanted to send in rec letters, but I had some questions. Obviously I don't know an alumna from each chapter, is it okay if I get an alumna who I don't know to write a letter of rec for me? Like do chapters look for recs from recent alumna or does it not really matter who writes it? Should I send one to each chapter, or only the chapters I'm really interested in? And what's the easiest way to get a good rec letter? Also, if anyone has any extra advice please lmkkkk!