Kodachi as a female version of Joker
(She's got the laugh down, she's a psychopath, plus she drugs all of her
food.  Now if it only was laughing gas instead of paralysis/sleeping
powder)

Nah. Poison Ivy.  It's too perfect.

She reminds me rather of Harley Quinn, from the Batman animated series..
Actually, Cheshire wouldn't be a bad choice either (gymnast who uses
poisons.  Rather obscure though...from the Teen Titans series)