Here's her story.
h/t Say Uncle.
Among Classical Greeks, amazon was given a popular etymology as from a-mazos, "without breast", connected with an etiological tradition that Amazons had their right breast cut off or burnt out, so they would be able to use a bow more freely and throw spears without the physical limitation and obstruction; there is no indication of such a practice in works of art, in which the Amazons are always represented with both breasts, although the right is frequently covered.
Antiope, Queen of the Amazons, preparing for battle. She looks perfectly healthy to me. I think that "right breast" stuff is a load of nonsense.