To many, Chloë Sevigny is the embodiment of downtown cool. Lured from Darien, Conn., by the Washington Square Park skate scene, she strutted seemingly naked in Sonic Youth’s 1992 “Sugar Kane” video while still in high school. Two years later, Jay McInerney famously anointed her the resident It Girl in The New Yorker. Now she’s back in the neighborhood where it all began, in Seth Zvi Rosenfeld’s “Downtown Race Riot,” presented by the New Group at the Pershing Square Signature Center.

Ms. Sevigny plays Mary Shannon, a ’60s flower child circa 1976, her bloom faded by children (Sadie Scott and David Levi) from two absent men and a heroin addiction that renders her useless against the escalating tensions outside her Section 8 apartment. But Mary has a plan: to bag a cool million from the city by claiming that lead paint has harmed her son. She’s aided by a lawyer (Josh Pais) she seduced at a cafe.

“Seth is from downtown Manhattan, and the language about the graffiti and the dialogue between the kids sounded authentic to me,” Ms. Sevigny, 43, said of the play’s allure, her rollicking laughter in startling contrast to her typically aloof characters. “And also, how poignant it is to talk about race in this context of the ’70s, when people were saying things that were so non-P.C. It’s an important play to put on right now.” Here are edited excerpts from the conversation.

Mary is a different character for you.

I made this pronouncement earlier in my career to never play a whore or a heroin addict, because I think it glamorizes them. Now that I’m in my 40s, I’m hoping it’s a different color. By the end, you see how desperate she is and how she uses her children. It’s a pretty dark portrayal.