Question

How does helen's appearance in the party make lavinia get rid of her superstitious belief in ouija boards?

Answer 1

Helen announces her presence in the party through the Ouija boards. This makes Lavinia highly suspicious of John. And next day she leaves the house. But, as John is speaking again with Helen, Lavinia walks in to the house. When she sees that Helen is actually a ghost she immediately forgives John. Additionally, she asks the maid Gladolia to burn the Ouija board.
Also, Lavinia realised that Helen is an apparition and there was no point believing in Ouija boards.