Well here's my thoughts on who could play as Poison Ivy and why...
Vanessa Hessler could be the best choice seeing she is really very hot. I would say she's got the attractiveness to play that role though I'd also like to see her as Sonya Blade in Mortal Kombat.
My other choice could be Emma Roberts. She's 5'2 (like the Animated counterpart) and she's done a good job playing the psychotic Jill Roberts. Now I'll just see her seductive.
Maybe Victoria Justice can take such a daring role though she isn't fair skinned but still, she can do.
Rhian Ramos Howell has that hot beauty. I'd love to see her seductive.
Rin Takanashi may be Japanese but she does have that "Western" appeal. Her acting as Arisa Yamauchi was pretty convincing.