Andrea's role in Mask of the Phantasm corresponds with that of the femme fatale from hardboiled detective fiction. Like classic femme fatales such as Brigid O'Shaughnessy from The Maltese Falcon, Andrea is a beautiful, deceptive, and strong-willed love interest for the main character. The fact that Andrea is secretly the main villain is another convention of this stock character.
Andrea also serves as a foil for Batman. The characters are very similar; they both don an intimidating costume and speak to the gravestones of their parents (as if holding a conversation with the deceased). The paralleling of their characters - most importantly the death of their parents at the hand of criminals - highlights how different they are: After her father's death Andrea chose to become a vigilante and killer, following a warped code of "eye for an eye" justice. Bruce instead chose to capture criminals and hand them over to the authorities, refusing to play judge, jury, and executioner.