Nisbett was last seen leaving her apartment in Cedar Park, Texas at 6:00 p.m. on December 14, 1991, on her way to a company Christmas party. She has never been heard from again. Her husband reported her missing on December 16, two days later. He said Nisbett had needed some time away and he thought she'd gone to Austin, Texas, but Nisbett's family said it is uncharacteristic of her to leave without warning. Nisbett was legally separated from her husband at the time of her disappearance, but they still lived together. Their divorce was to become final in January 1992.

In January 1992, police searched Nisbett's home and found her blood in the master bedroom of her apartment. It appeared as if someone had tried to clean it up. Based on the amount of blood found, authorities feel Nisbett is deceased. An anonymous phone call lead police to her brown 1987 Dodge Aries staton wagon in a parking lot off of Mopac Boulevard on February 8, 1992, nearly two months after her disappearance. The vehicle had apparently been parked there for several weeks.

Foul play is suspected in Nisbett's case; it remains unsolved. She was employed with the Texas Municipal League in 1991, and had three young children.