It was always a red rose.
In the aftermath of a failed heist. After the fighting had gotten too hot and the goons were down. He'd send her to distract Batman. It was always the same, he would 'go get the car' and she knew, she knew, he wouldn't come back for her. She knew and yet she still hoped. Even while she was being hauled back into Arkham. Even when the others whispered about her; about what he'd done to her, and like always they would question 'what could she have been thinking?'.
If she was honest, sometimes even she didn't know what she'd been thinking. She'd cry herself to sleep those nights; cursing that she'd ever heard the name Joker. Silently mourning what she could have been and what she could have had.
When she woke up though... beside her would be a beautiful red rose and it would make up for everything.