Matilda would win this battle. Poison Ivy would get a shock when she attempts to use her plant powers on Matilda, only to have Matilda fight back with her powers of telekinesis, thus causing Ivy to realize exactly why Matilda is a Lady and a Scholar. This would be true — especially when Matilda tells her about Miss Trunchbull, who was formerly the principal of Crunchem Hall Elementary School and terrorized the students until Matilda came along and helped them find their courage to fight back against Miss Trunchbull, finally driving Miss Trunchbull away from Crunchem Hall for good.. :)