Two examples in the text of Wuthering Heights that show that Nelly is reading Isabella's letter to Mr. Lockwood are in Chapters 13 and 14. In Chapter 13 Nelly tells Lockwood about a note Isabella sent to her brother announcing her marriage to Heathcliff and asking forgiveness and reconciliation. Then Nelly says that she herself received a long letter about two weeks later (a fortnight, or fourteen days).
Nelly goes on the say that she still values it and says, "I'll read it: for I keep it yet." Nelly goes on to say, "'Dear Ellen, it begins, - I came last night to Wuthering Heights...." In Bronte's construction, Nelly's voice blends in with Isabella's own voice because it is Nelly's voice that says "it begins," but there is no textual punctuation orother signification that this is so.
In Chapter 14, Nelly steps out of the reading and tells Mr. Lockwood, "As soon as I had perused this epistle I went to the master." These steppings in and out of the epistle (1) in her own discourse and (2) in her conversation with Lockwood, are demonstration of the mechanics of intertextuality in which separate texts influence each other.
Here are some quotes that show Nelly is reading Isabella's letter to Lockwood...
Dear Ellen, it begins—
The "It begins" on the letter shows that Nelly is making sure Lockwood knows that she is going to start reading the letter out to Lockwood.
Thrushcross Grange in twenty-four hours after I left it, and is there at this moment, full of warm feelings for him, and Catherine! I can’t follow it though —(these words are underlined)—
"I can’t follow it though —(these words are underlined)" is Nelly telling Lockwood the difficulty of reading through that part of the letter.
When Nelly is done reading the letter she tells Lockwood how she went to Edgar right away and told him of Isabella situation.