OK, Deathstroke would need feats for resisting poison à la Wolverine or Deathstroke to prevent a 10-count at least against Ivy's poisons.
Deathstroke has no such feats.
Now, in a scenario where Ivy doesn't know he's coming, Slade could maybe find a way to spot her from a mile off and snipe her out of range or something, but if she DOES know he's coming, there really isn't any reason for her to show her face at all.