Darkness curse gonna darkness curse. That isn't too shocking. Crack theory time: Witch Elsa is trying to get her to give up so that she can slide in and have an Evie to herself.
Id be quite surprised if that was the case, cuz I dont think thats what Dorothee wants. To me this seemed like the curse driving Elsa to despair, but I have no idea to what end. I get the feeling that Elsa drank the potion again, thinking that Dorothee would be better for Evie, but how would that benefit the curse?