She's a young thug who runs around with fellow criminals Nick and Billy Hill. The film begins with the former man attempting to buy a cup of coffee at a convenience store. When the clerk manages to be difficult, Dallas shoots her multiple times, and it is then implied that she and the two men shoot a police officer who enters soon after.
Later on, Nick stashes some drugs in the home of an old buddy of his, protagonist Casey. Dallas shows up at the man's house to retrieve it, entering right in the middle of a meeting between this friend and Doctor Jarvis: a man who has come to determine if Casey is stable enough to adopt a child. Dallas act and talks vulgarly around Jarvis, and then tells him a story about Casey's criminal past, prompting the doctor to leave in disgust.
With that obstacle out of the way, Dallas pulls a gun on Casey, ties him to a chair and begins to interrogate him. After explaining that he discovered the drugs and sent them swimming down the sink, the women tells him that it's the $2,000,000 that she's after; money that, until that moment, Casey was not aware of. To eat up time until nick arrives, she decides to have sex with her prisoner before killing him. However, the impatient Billy Hill enters and shoots her in the head before that happens.