She thinks this is her fault. Rey is amused with the situation. It is very new and exciting for her. Eventually, Mia kicks her shoes off. Then Mia uses her toes to grip Rey's gag and pull it down.
Mia walks in calling out for Rey. She thinks Rey has snuck off on her own, defying her orders. She walks around a bit looking for Rey. Mia doesn't see or hear her. Mia walks out of frame.