I think you're spot on. They're building a nice back and forth right now, becoming friends as well as doctor and patient. Once that bond is solidified we can totally exploit it.

Harley's been really well behaved since she arrived, I mostly blame it on her gem being a sort of emotional and mental anchor for her, but also because Waverly Bay is so damn chill compared to the hustle and bustle of New York and Gotham.

But sooner or later, that homicidal loon is gonna peek out again and it'll be interesting to see how.