Final answer:
The correct form of the -ar verb is enseñ
Step-by-step explanation:
The correct form of the -ar verb in this sentence is enseña.
When conjugating the verb enseñar (to teach) in the third person singular, we use the form enseña.
So the correct sentence would be: La maestra es buena, ella enseña la clase todos los días.
Learn more about Conjugation of -ar verbs in Spanish