Example paragraph:
I wake up at 6 a.m. during the week. My sister wakes up later because her classes start at 10 a.m. She drinks coffee in the morning while I make tea. After breakfast, we both walk to the bus stop together.
Sentence 2:
The predicate (main verb) is "wakes up", which is third person singular.
Who wakes up? = "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 "drinks", also third person singular.
Who drinks coffee? = "she" is a pronoun used as a subject, and it is third person singular feminine.
Its antecedent is the noun "sister" in sentence 2, which is also third person singular.
Therefore, the pronoun and its antecedent agree.