Final answer:
A comma is needed after the word 'boring' to separate the direct address from the rest of the sentence.
Step-by-step explanation:
In the given sentence, a comma is needed after the word 'boring.'
The corrected sentence would be: 'We thought the movie was boring, Mrs. Washburn.'
The comma is necessary to separate the direct address ('Mrs. Washburn') from the rest of the sentence.
Learn more about Punctuation in English sentences