Mayfly was contracted by Ares Buchanan to assassinate Wonder Woman.  Despite having previous opportunities she bypassed them to engage Diana directly at the mall where Diana and Etta Candy were shopping for a wedding dress (for Etta.)  Prior to her attacks, Wally West showed up and informed them that Diana was being targeted.   With her superhuman speed, she was able to nearly kill Diana on several occasions, but on two occasions underestimated Etta.  In the end Diana shoots an arrow into her rifle causing a jam, though Diana herself takes numerous hits and is hospitalized.  Meanwhile Mayfly was taken into custody.  While under imprisonment Mayfly threatens to reveal what she knows to the authorities in a plea bargain.  After being visited by Ares Buchanan's lawyer, Mayfly decides to escape instead, but she was unknowingly being manipulated to believe she could escape when in fact it was almost assured that she would die, as she was running at high velocities in tight spaces and as she is a hemophiliac.  In the end Mayfly runs into a wall at full speed, accidentally killing herself. 

In addition to her super speed (which was shown to be at least as fast as the Flash) Mayfly was an expert markswoman, able to shoot the Flash as he was running at full speed.  She also incorporated some optics into her helmet.