Leo 's acting debut came in 1984 , for which she was nominated for a Daytime Emmy at the 12th Daytime Emmy Awards for Outstanding Ingenue/Woman in a Drama Series for '' All My Children '' . Following this , Leo appeared in several films , including the lead role as a straitlaced girl named Cookie who succumbed to prostitution in '' Streetwalkin ' '' , '' A Time of Destiny '' , '' Last Summer in the Hamptons '' , and '' Venice/Venice . '' She also had several appearances on television , most notably her role as Det. Sgt. Kay Howard on '' Homicide : Life on the Street '' until 1997 . Three years later she reprised her role in the television movie , '' Homicide : The Movie '' . After a brief hiatus from acting , Leo 's breakthrough came three years later in the Alejandro González Iñárritu film , '' 21 Grams '' released to critical acclaim . Leo appeared in a supporting role alongside Sean Penn , Naomi Watts , Benicio del Toro and Clea DuVall . Leo shared a Best Ensemble Acting award from the Phoenix Film Critics Society in 2003 and the runner-up for the Los Angeles Film Critics Association for Best Supporting Actress
12th Daytime Emmy Awards
12th Daytime Emmy Awards
Melissa Leo