Correct answer:
nos miramos
Nos is the reflexive pronoun that matches the first person plural. In Spanish, we use Reflexive Pronouns with a verb to point out that a person carries out an action to or for himself or herself. So Ana and I (Ana y yo) carry out the action here for ourselves. On the other hand, miramos is the conjugation of the verb mirar for the first person plural in the simple present. Finally:
Ana y yo nos miramos en el espejo
