Nancy Spungen was a model student, who became Sid Vicious' Girlfriend. After meeting him, they both become addicted to chocolate (replacing drugs in the episode), wich turned their lifes out of control. When Sid destroyed one of the Sex Pistols show, she made him quit the band and start a solo career, with she composing his songs. Nancy is similar to or was played by Lisa Simpson or is who Lisa Simpson disguised herself as.
Behind the Laughter
In real life, she wasn't a model student. She was actually a rebelious teenager that ran away from home and moved to New York, where she met Sid. She was killed by Sid himself in October 12 1978 with a fatal stab in the abdomen.