Non-Catholics Need Annulments Too

Yes. Marriage is the exchange of consent to be in a fruitful, loving, and committed relationship until death do you part. When a man and woman publicly make these vows, those vows are presumed valid unless proven otherwise. Your brother’s fiancée is presumed to be validly married at her wedding in the Episcopal ceremony. She would need to apply for a declaration of nullity (i.e., an annulment) for that marriage before she would be able to be married in the Catholic Church.