Peppermint shrimp are said to be hit or miss, but I have always had luck with them. Dipping it will do nothing to kill the aiptasia. An easy fix would be to inject it with one of the aiptaisa products on the market (Joe's Juice works well and it comes with a syringe) or inject it with kalk slurry, lemon juice, or even boiling water. The surrounding zoas may get irritated, but they should recover nicely.