RORY (referring to Louise and Madeline greeting her): Normal, friendly, no acts.
LORELAI: Wow, you’re the new “Heather”.
Lorelai is referring to the 1988 black comedy film Heathers, directed by Michael Lehmann. The film stars Winona Ryder as Veronica, a popular girl at an Ohio high school, who hangs out with a clique of beautiful, wealthy girls all named Heather (Shannen Doherty, Lisanna Falk, and Kim Walker).
Despite being the most popular students at the school, the Heathers are feared and hated, and Veronica wants to get away from them. When a new student named JD (Christian Slater) becomes Veronica’s boyfriend, he manipulates her into helping him kill one of the Heathers and making the death looks like suicide. After the death, the next Heather in line assumes her role. Lorelai is saying that with Paris apparently toppled from her role as head mean girl, Rory can now step into her shoes.
Heathers was widely praised by critics on release for its cynical and subversive tone, and the director and screenwriter both won awards. It wasn’t a big success at the box office, but developed a cult following after being released on video in 1989.