Hayden was a diplomat who lived in Paris due to her job. She met Rossi there while he was on a trip and the two hit it off. They started a romantic relationship, which eventually culminated in marriage. However, after a few months, Rossi, ambitious at the time, wanted to become known to the world and found Hayden's job to be a real burden to him. That, coupled with the demands of his job, caused him to divorce her, but not before she was impregnated with his child. Rossi returned to the U.S., all the while unaware that Hayden was pregnant and he was the father. Even though they kept in touch for a time after the divorce, Hayden decided not to tell him of her pregnancy due to the fact that his job would very likely keep him away from the family all of the time. She later remarried and gave birth to a girl, which she named Joy, who was raised into believing Hayden's current husband was her biological father. However, the lie was exposed after Hayden's husband came down with terminal cancer and confessed the truth to Joy. Joy confronted Hayden about it, and she revealed to her who her real father was.
On Criminal Minds
Prior to her physical appearance in Season Ten, Hayden was mentioned several times in the show's progress by Rossi, though not by name. During those references, she is usually mentioned alongside Rossi's other ex-wives. The first detail attributed specifically to her was given in the Season Nine episode Strange Fruit, when Rossi revealed she was African-American to serial killer Charles Johnson. Finally, in Fate, she makes her first physical appearance in flashbacks throughout the episode and is prominently mentioned by both Rossi and Joy.
Hayden reappeared in the present day, in the Season Eleven episode Inner Beauty. In the episode, she has an awkward reunion with Rossi at her son-in-law Shawn's house before Rossi leaves to help the BAU investigate a case. At the end of the episode, Rossi returns to Shawn's house and reconciles with Hayden. She reappeared in the season finale episode The Storm, where it seems like they have resumed their relationship. Following the conclusion of the latest case, Rossi invites her, among others, over to a party at his estate. During the celebration, the BAU gets a call about thirteen escaped serial killers, and Rossi reluctantly leaves Hayden alone.