One of the main issues I was encountering with this character was having her hair turn from red to green as it becomes vines. I tried a gradient layer style over the hair texture, I think its the most successful solution so far.
Im still struggling with the colour palette and textures. I think the colours here could work well in the line up with Harley, both characters have fairly dull colour pallets but then occassionaly there is some bright colour. In Ivy's case its her skin, In Harley's case its her hair and eyes. Also the joker will have bright sections of his suit and cat woman has bright either yellow or green eyes to contrast with her black suit.