I leave for work at 7:00 am. My sister never goes straight to work. She goes to my parents house first, she always helps them because they are very old.
Sentence 2: The predicate is "goes", which is third person singular. "sister" is a noun used as a subject, and it is third person singular. The subject and verb in this sentence agree.
Sentence 3: The first predicate is "goes", which is also third person singular. "she" is a pronoun used as a subject, and it is third person singular. Its antecedent is the noun "sister" in sentence 2, which is also third person singular. Therefore, the pronoun and its antecedent agree.
the second predicate is "helps", which is also third person singular. "she" is a pronoun used as a subject , and it is third person singular. and also the pronoun and its antecedent agree, which it is "sister" a third person singular.