Some people are wondering

Since i've seen multiple people confused, i'll copy-paste my explanation on why the title is "The perks of being a villain";

She transmigrated into a transmigration novel, so the original story the pink haired girl was the MC and Fredia was a villain, in the novel some girl gets transmigrated into Fredia and becomes the MC instead, so Isabela + their family becomes the villains of the second version, then OUR girl gets transmigrated into Fredia instead and is now the MC.

So there are three versions of the story
1.The original novel
2.The novel our Fredia read
3.The current story

Tldr; In the original novel that the original transmigrated girl read, Fredia is a villaness. After she transmigrated she became the MC instead and her family are the villains.

OUR Fredia read the second version of the story, with the transmigrated girl as the MC.

Hope this helps