Pamela Isley. Eco terrorist, human hater, manipulator.
In this reboot, she's going to be the mentor of Harley Quinn. But she'll be the mentor in the same fashion as Hannibal Lecter was in Silence of the Lambs. She remains in Arkham for the first few episodes, with Harley sneaking in to consult with her.
I think Poison Ivy is taken to lightly in most stories which is why I'm treating her like a weapon of mass destruction which she is. Using her powers she can kill in the most vile and devastating ways. She could level a city in short order. Hence she's kept under an airtight lock and key.
She's forced to provide herself with her own oxygen as her powerful pollen could seep through an air vent. So her clear enclosure front appears to look in on a terrarium. Without sunlight though she's only able to grow normal plant life. Nothing strong enough to break herself out. Hence she's trapped pretty well.
When Harley Quinn first sneaks in and has her life changing conversation with the Joker she sees an opportunity. She overhears Joker's words to Harley.
After her first outing as Harley Quinn she comes back to brag to Mister J only to find his cell empty. A voice calls to her from the door next to his. Harley edges over and sees a softly colored green woman (the hooded version) standing at the glass.
He escaped. He does that you know. You'll never pin him down, that one.
Harley then comes back several times afterward getting advice and guidance from Ivy and each time Ivy tries to convince her to set her free.
Eventually Harley gives in and opens Pandora's Box.
For her look I wanted to make her really viney, etc but then I realized that the best versions of her are the simpler ones. So I started back from scratch after several drafts and came up with this forest nymph like look for her that I ended up liking.