Here's why:
* Subject: The subject is "My sister," which tells us who the sentence is about.
* Predicate: The predicate is the part of the sentence that tells us something about the subject. In this case, it tells us that "My sister" is the "captain of cheer-leading squad."
However, the sentence is grammatically incorrect. It should be "My sister is the captain of the cheer-leading squad." The verb "is" is needed to complete the predicate and make the sentence grammatically correct.