Sergeant Selma Wells is a police officer of the LAPD.
Sergeant Selma Wells was with a group of cops singing "Silent Night" in preparation for Christmas, possibly for the annual parade. She made sure everyone was in rhythm and hits one cop, Cooley, lightly in the stomach with her baton when he was out of pitch. They continued to sing even when they passed down the hallway of Captain Murphy's office.
Selma Wells appears again in the third film. When Leo Getz wanted to see Martin Riggs and Roger Murtaugh, she would not let him through without a pass. Murtaugh told her he's with them and only then did she let him pass.