Harley had escaped from a few things in her life - a family filled with deadbeats was the first and most prominent of her life. She had escaped a lifestyle of goodness by meeting Jack, though she never had entirely snuffed out that spark of genuine purity.
"Ya could say I've been in tha slamma a time a two. In an outta Arkahm some, as well. Can't help it, really. I ain't a bad person, yanno, just got a few bad habits that are hard ta shake. Hard bein' on ya own and tryin' to make it in a world that's always against ya."
Harley didn't have to lie to Maleficent. She had a feeling the woman could tell, and they'd been up front with each other so far. Just because she'd been in some trouble didn't mean she was a bad person.