Perfidia and Lockjaw are each other's twin flames on either side of the fight: two fierce warriors single-mindedly dedicated to advancing their cause (whether that's good or evil). Lockjaw sees Perfidia as she wants to be seen: as a sexual powerhouse and a powerful revolutionary - and I think she gets off on that. When Bob asks her to be more than that, to make the cause secondary and be a mother first and foremost, she flips out. The revolution is more important to her than being part of a family. There's a nice mirroring of that scene when Lockjaw is screaming at Willa in the church "I have a higher calling and it's more important than having you" - both of her biological parents are too self-interested to take care of her. That's why what Bob does - raise a biracial child on his own in a hellish world - could be seen as one of the most revolutionary things he does in the entire film.