After she turns into Poison Ivy, Pamela puts on a wig and big glasses and frumpy clothes to disguise herself when announcing her plans to save the planet at the Gotham Observatory. Why does she need make herself look ugly and act crazy? Wouldn’t Bruce and the guests at the observatory take her plans more seriously if she showed off her good looks and acted like a rational sane individual?
The problem is, Ivy didn't look like her old self anymore. She couldn't let anyone know that the real Pamela Eisley had "died" in South America, and in her place was a sexy, flame-haired, plant/human mutant bent on destroying humanity. She had to put on a show with the dual identity thing. It was all an act. Ivy knew that Bruce Wayne would not change how his company worked, but she had to know for sure while pretending to be the innocuous, not-taken-seriously Dr. Eisley. She knew they would dismiss her as a nutty greenie, and it's a great way to throw suspicion off her....for a while.
Didn't take long for Bruce to find out who she was when the real Ivy started wreaking havoc on Gotham alongside Mr. Freeze. Batman always does his homework on his foes.
Maybe Pamela could have used her pheromone dust and charms on Bruce and invite him on date to discuss the proposition and she could mind control him. Seducing Bruce, would allow her all the money she would ever need.