What change, if any, should be made in this sentence? “Stacy and her twin sister, Sally, is always being mistaken for each other.”

Flashcard 14 - High School English II: Writing Flashcard Set for the STAAR test

The word is should be are.

The sentence has two subjects, Stacy and Sally, so the verb must also be plural: are, not is.

All Flashcard Sets for the STAAR test are now available as downloadable PDFs