Continuity mistake: Batgirl's cape changes length throughout the episode. It goes from reaching her ankles to her hips.
Other mistake: When Catwoman scratches Batman's face in the flashback, her fingers and claws stretch comically.
Continuity mistake: During the flashback, Catwoman's whip disappears and reappears on her belt in a couple of scenes.
Continuity mistake: When she was pulling Daggett up, Batgirl briefly gains pupils when she says "Catwoman, wait."
Continuity mistake: Harley's shoes are poorly drawn when she dances in Dr. Leland's office.
Continuity mistake: Catwoman/Selina gains and loses her pupils throughout the episode.
Continuity mistake: Batgirl and Catwoman briefly gain pupils in one shot of them during the Stacked Deck fight, despite not having any throughout the episode. (04:00:39 - 04:41:24)
Answer: She escaped off-screen and created a copy of herself to fool everyone.