Notice the tagline says "Evil Wears Many Faces" ? At first, one could say this refers to Leatherface's masks. But examining from the plotyou'll notice Leatherface and his family are not the main antagonists of the film, rather Burt Hartman and his goons, the film also has plenty of Asshole Victims and the protagonist has a Start of Darkness.
When Heather reads Verna's letter, one of the sentences was "He's yours now". The brilliance of that scene comes when you take into account that Verna is played by Marilyn Burns, who played Sally in the original. And since the sequels that are rumored to be in the works are set to continue Heather's story, this is a symbolic Take Up My Sword from one Final Girl to another.
Heather siding with Leatherface seems makes no sense unless you think about it. She's caught between two evil men,one will kill her due to her family and the other tried but stopped because she ''is'' family. Small wonder she makes the choice she does.
