She included this anecdote to increase support for the argument.
To justify this argument, the author presented supporting sentences that show how and why the argument is correct. To strengthen these supporting sentences, he shows that she knows the story of Romeo and Juliet and even presents the anecdote that shows when she watched the play staged by the Royal Shakespeare Company.
More information about "Romeo and Juliet" at the link:
https://brainly.com/question/5025530