Sam standing up to her stepmother (Fiona) in the diner and later having her arrested. Rhonda threatening to beat up Fiona.
The entire diner staff gets this as well. After Sam decides she's had enough of her stepfamily and quits, Rhonda follows after with her threat of pummeling Fiona for everything she's done to Sam. The rest of the staff quit alongside Rhonda, and the customers walk out as well. The only reason any of them stayed and dealt with Fiona was for Sam.
Fiona manages to avoid jail time for hiding Sam's dad's will by working off her debt mopping floors at the diner under the eyes of new boss Rhonda. Better yet, her daughters are working right with her and we see all three falling over themselves on the floor with Rhonda smirking.