Well, I was and still am a Serpent. They put me through college. Law school.
~ Penny Peabody to Jughead Jones.
Penny Peabody is a Southside lawyer from Riverdale affiliated with the Southside Serpents. She becomes the lawyer for the Jones family after F.P. Jones is brought up on criminal charges and facing jail-time.
Penny Peabody's exact early life is not known, but she was apparently a member of the Southside Serpents, who, in her own words, put her through College and law-school. As such she retains her loyalty to them, and gets payment from them in the form of "favors" rather than cash payouts.
After F.P. Jones is brought up on charges of conspiracy and tampering with evidence in a criminal investigation, he is threatened with jail-time if he does not name names. F.P. refuses to do so, and is thusly incarcerated. Not long after, a desperate Jughead goes to Penny Beabody for legal help, which she provides, but she warns Jughead Jones that she will be expecting a favor from him one day in return, the first sign of her not being on the up and up.
Sure enough, Penny later contacts Jughead to call in her favor, also informing him that, after Jughead's father was jumped in the prison shower by vengeful Ghoulies, he is badly hurt and hospitalized. Penny has Jughead transport a crate containing an unknown substance, assuring Jughead that the job is reasonable and that it is a one-time deal. However, when Jughead and Archie transport the crate to the location Penny directed them to successfully, they discover that it is actually a crate of drugs, and that the warehouse in Greendale is the sight of a drug deal. Worse for Jughead, is that Penny has apparently told her partners that Jughead will be her regular delivery-boy from here on out. In other words, it is not a "one time deal". Checking up on his father in prison, Jughead then discovers yet one more piece of bad news: that his father was never jumped or beaten or hospitalized, meaning that Penny lied to him and tricked him into delivering the drugs under false pretenses. He angrily confronts her about this, but she reveals that she has footage of him and Archie transporting the drug crate, and warns him that if he fails to comply with her going forwards, she will send the footage to the police, essentially putting Jughead in her pocket indefinitely.
However, after Jughead alerts his father to Penny's blackmailing him, the latter not only resolves to remain with the Serpents, but Jughead later rallies the younger Serpents to kidnap Penny and take off her Serpent tattoo, symbolically stripping her of her membership within the gang.