Rem (レム, Remu?) The female shinigami who first gives Misa her Death Note and trades her for the Shinigami eyes. Similar to Ryuk, Rem possesses two Death Notes; however, she purposely gives one of them to Misa Amane. Rem inherited her second Death Note from Jealous, another shinigami who died when he saved Misa's life, and thought it only right to pass it on to Misa. Rem inherits Jealous' love for Misa as well and is prompt to defend Misa even at the cost of her life. Rem shows this when she states that she will kill Light if Misa dies before her time. this is from wikipedia,i hope this answers your question
I heard that the shinigami have "genders" but they don't mean anything because they don't have sex. It's in one of the rules. Who knows? Maybe she just sorta butchy? That or the people in the movie didn't want to bother with a more feminine sounding person.
