Who is Lady Arete from Gates of Fire and what is their importance?

Once married to Dienekes' brother, Lady Arete is now his wife. Dienekes was her first love, thus, after her first husband is killed in battle, she insists upon their marriage. Lady Arete unknowingly makes Dienekes eligible for the 300-Spartan force when ahe takes Rooster's son as her own in an effort to save the young boy's life.