The isn’t actually the first hint at Ace’s paternity.

↓ Transcript
Pixie: Why doesn't she understand that I still love her?
Mama Gibs: Isn't the issue your relationship with Steve?
Pixie: That was never a problem before.
Mama Gibs: Sweety, he beat you so badly, you were in the hospital for a week. And I doubt that was the first time he hit you.
Pixie: He was under a lot of stress. And he says he's learned his lesson. It won't ever happen again.
Mama Gibs: Oh for . . . I've heard that before, Dear. Guy's like that never change.
Pixie: How would you know?
Mama Gibs: Let's just say there's a reason Ace will never know who his father is.