Lena Luthor is the name given to two characters in DC Comics, the first Lena is Lex Luthor's younger sister while the second Lena is Lex's daughter who was named after her aunt. Both Lena's in the comics are the few people Lex cares about yet both his sister and daughter have a distant relationship with him due to his status as a supervillain.
The first Lena Luthor was portrayed by Katie McGrath in CW's Supergirl. In the show, Lena befriends Kara Danvers/Supergirl, unaware of the latter's true identity while trying to redeem her family's name due to her brother's villainous actions.