Mary Anne was the name used by a salt vampire who dated Commander Jack Ransom with the intention of extracting the salt from his body.
She took on the appearance of an attractive young blonde Human woman, when she was aboard the USS Cerritos and with Ransom. In both her Human and natural forms, Mary Anne wore a blue sleeveless dress and had a gray skirt. Her eyes were yellow and her hair was white while in her true form.
Ensign Beckett Mariner told Ransom that he was dating a salt vampire, but he refused to believe her, telling her that salt vampires became extinct over a century ago.
When he walked off with her, she changed back into a creature and tried to assault him, and he screamed "Salt vampire!"
Later, when Ensigns Brad Boimler, Sam Rutherford, D'Vana Tendi, and Beckett Mariner were in what they thought was a courtroom, they believed that their senior officers were on trial.
While explaining to Clar (whom they assumed was the prosecutor) that the senior staff wasn't always aware of what was going on, Boimler cited this story about Ransom and his salt vampire "girlfriend" as an example of just how clueless they could be at times, as they were only Human, and that one of Starfleet's main purposes was to explore the unknown. (LD: "Veritas")