Tabitha Galavan was dead after she was stabbed in the heart by Oswald Cobblepot.
So you thought. Hugo strange got hold of her body and lets say resurrected her.
She awoke not knowing who she was. Hugo Strange gave her a new name and identity. She was now Tahliah. You one day see her walking the streets and call out tabitha at her. She turns around and faces you "who is tabitha?"