Final answer:
Without the specific context of Eleanor's character or events from 'The Haunting of Hill House', it's not possible to determine the cause of her happiness from the options provided. One would need to refer to the novel's plot and character development.
Step-by-step explanation:
The question appears to be related to the novel The Haunting of Hill House by Shirley Jackson, which makes this an English subject topic. However, without additional context about Eleanor's character or specific events in the story to which this question refers, I cannot provide an accurate answer to the cause of Eleanor's sudden happiness. The options provided (haunting, new friend, surprise gift, lottery) suggest different scenarios that could occur in a variety of narratives. Typically, sudden happiness in a character could be due to a positive event or realization, but to identify the correct cause from the options given, one would need to refer specifically to the plot and character development of The Haunting of Hill House or the relevant text in question. Since I am unable to confirm the correct context, I must refrain from providing a definitive answer to this question.