Final answer:
The provided excerpts do not correspond to the question about Cathy's plan and Nelly's response in 'Wuthering Heights.' Due to the lack of relevant context from the novel, a precise answer cannot be provided.
Step-by-step explanation:
The provided excerpts do not directly relate to the initial question about Cathy's plan and Nelly's reaction; moreover, the question appears to be referencing characters and a plot from Wuthering Heights by Emily Bronte, which is not included in the provided excerpts.
Without the right context from the novel, it's not possible to accurately address the question about Cathy's plan to "break their hearts, by breaking my own" and why Nelly would not take her seriously. Cathy and Ellen "Nelly" Dean are characters in Bronte's novel, involved in a complex intergenerational story filled with themes of revenge, love, and social class.
In case the excerpts provided were intended for different questions, then more accurate sources of information need to be presented to appropriately answer Cathy's plans and Nelly's response from the novel Wuthering Heights.