In the cut-scene introduction to ballistic trauma, we see Papa Caesar on his mobile phone telling someone that Detective Washington and his associate (Agent G) are on their way to the hospital. Papa Caesar explains to the person on the phone that he has a plan to eliminate any evidence of their evil plot. Here we see the Screamer suspended in a large tube of liquid.
Throughout the level the Screamer can be seen stalking the players throughout the hospital, randomly popping up in various windows and peering through certain doorways. During these 'cameos' the Screamer cannot be harmed nor can she harm the players.
At the end of Ballistic Trauma, the Screamer is faced by our heroes in the bowels of the hospital in an empty, partially flooded operating theatre.
In the 'Director's Cut' version of the level, Detective Washington and Agent G encounter the screamer prior to the actual fight. She is crouched in the corner of a dark corridor in the hospital and when they approach her, she stands up and displays her lovely singing voice - smashing windows and sending our heroes across the corridor into unconsciousness.