Thirty-one years after the tragic death of 23-year-old star Selena Quintanilla, her legacy endures, with fans visiting her grave in Texas as her killer remains behind bars.

Suzette Quintanilla -- the sister of late music icon Selena Quintanilla-Perez -- is suing Shein, claiming the company has been splashing her famous sister's face all over clothes sold on its website without any permission ... TMZ has learned. In…