On page 263, Legs calls Mrs. Kellogg and her religious daughter, Marianne, class enemies. In the book the author states:
Rich man's wife, rich man's daughter. Class enemies, they were. All knowing-unguessing.
Mrs. Kellogg is the wife of the industrialist Whitney Kellogg, who Margaret and the rest of the Foxfire gang are planning to kidnap and hold to ransom to finance what they call the "final solution." To them, Whitney Kellogg and his family represent the 50s' ideological structure they are fighting against; that is, a traditional family unit lead by an all-powerful patriarchal figure.
Leg's hatred of the Kelloggs is not straight-forward. Coming from a broken home, where she had to make her own way in life, unlike Marianne Kellogg. Thus, her hatred is mixed with feelings of envy. She even admits that Marianne is a kind-hearted girl whom she hopes will one day "reject her background, come live with Foxfire." The reader gets the feeling that this would be as much a victory for Legs as the "final solution."
Legs says that Mr. and Mrs. Whitney Kellog, along with their daughter Marianne, are class enemies on page 263 in part 5, chapter 3 of the edition published by Dutton in 1993.
Joyce Carol Oates writes:
Rich man's wife, rich man's daughter. Class enemies, they were. All unknowing--unguessing.
This attitude is what leads Legs and Violet to kidnap Whitney Kellogg, Jr. They use Violet's beauty to lure him into the trusting them; she looks like Snow White.
They think that it will help them with the money that they need to secure their future and help protect women from bad men and other women and girls who are part of the problem. It doesn't work out as they plan, however: Whitney finds God and doesn't cooperate. He's shot during the kidnapping and it sends them running from the police. They don't get the money for the ransom. Ultimately attempting to kidnap a class enemy and use him for ransom becomes the end of the gang.
Your answer will depend upon which edition you have. What I have is the 1993 edition, so the term "class enemies" is on page 263 of Part Five, Chapter Three (which is titled "Windward").
After being released from Red Bank (the correctional facility for girls), Legs crafts a plan to abduct Mr. Whitney Kellogg (a multi-millionaire businessman) for ransom. She befriends Marianne Kellogg, Mr. Whitney's daughter, who invites her to the Kellogg family's Greek Revival mansion several times. Marianne is a participant in the Big Sister-Little Sister program of the United Churches of Hammond Auxiliaries; she first meets Legs at the Red Bank correctional facility during a visit. In Part Five, Chapter Two, Legs admits that she is only nice to Marianne because she hopes to profit from the acquaintance. Ruthlessly, she characterizes Marianne as a flightless bird and herself as a "bird-eating mammal" who is ready for the kill.
Meanwhile, the "Windward" chapter (Part Five, Chapter Three) describes Legs' first and second visits to the Kellogg mansion. During her first visit, she meets and engages in polite conversation with both Marianne and her mother, Mrs. Kellogg. Legs refers to them as "class enemies." To Legs, both Marianne and her mother represent a privileged class of women who have seemingly never suffered any deprivation in their pampered lives. Yet, even as she envies their lives of ease, Legs also rejects their condescension.
Despite her contempt for Marianne and her mother, Legs knows that she must act the part of the "reformed" girl. She does this admirably, pausing often to acknowledge and to praise the famous Kellogg charity. Privately, however, Legs deems the women "class enemies," who are "unknowing" and "unguessing" of her true thoughts regarding them. Again, in my edition, the "class enemies" reference is on page 263 of Part Five, Chapter Three.