The character of Desiree, as created by Kate Chopin for "Desiree's Baby," is a relatively unknown character. Her history has been assumed by both her "adoptive parents," (the Valmondes) and Armand. Having found her by "the big stone pillar," the Valmondes immediately feel in love with the child. Raising her as their own, it was of no surprise that Armand fell in love with the girl (years later) as she was next to the same pillar she had been found at.
Given that Desiree was a very compassionate character, her nature balanced the character of Armand. He, prior to their marriage, would punish his slaves. After the marriage to Desiree, and the birth of their child, Armand was different--the birth and marriage had "softened Armand Aubigny's imperious and exacting nature greatly." Therefore, the marriage to Desiree was perfect given it had made him a more compassionate man.
Outside of Armand's change, Desiree brought a warmth to L'Brai. Although superficially rundown, the change which happened within the walls of the plantation was extreme. The home seemed to glow (with both the love between the couple and the love they had for their child).
One last thing which shows how Desiree was the perfect wife for Armand was the outcome of the story. Armand is very proud that he possesses one of the "oldest and proudest" names in Louisiana. By using Desiree's unknown history as a scapegoat, Armand is able to keep his name from being tarnished (given his mother's ethnicity). Essentially, Desiree is the perfect wife because she is able to allow Armand to keep his family's secret.