Question

How does the ghost undermine the narrator's faith in his ability to write ghost stories?

Answer 1

Helen said that she always sit on the shoulders of Hallock ND gave him ideas for his ghost stories
she was constantly saying this ND convinced him that she only helped him 2 write the story

Answer 2

Helen constantly told the narrator that she has helped him to write ghost stories,she told him that she used to lean on his shoulders and give him ideas when he was thinking hard to write a ghostly story. She tells him that if she has not been there for him he couldn't write good ghost stories.
:) Hope this Helps !!!