Zee figured Dinah would tell her about the Joker stuff when she was ready. That guy was bad news at the best of times. When he got into your head it was nightmare worthy.
Of course then Dinah was excusing herself and hugging Zee who blinked in surprise then snipped out a whisper in her ear while faking a smile. "I am going to kill you for this you realize." But she wouldn't stop her friend from leaving. For all Zee knew Dinah needed to be somewhere.
"Gee, thanks." She gave Dinah a wry smirk as she let her go.