Arias was living with Fernandez when he was killed in a tragic boating accident off the coast of Miami Beach on Sep. 25, which also claimed the lives of two of his friends. The couple had announced that they were expecting their first child just five days before the crash.
Arias said that the birth of her daughter has "not taken any of the pain away, of course, because that's always going to remain. But she's definitely brightened up our lives."
"A lot of people were anticipating her arrival," she added, "because at the end of the day, it's a little piece of him that he left behind for us."
Fernandez, 24, was born in Cuba and defected to the U.S. in 2008, where he went on to join the MLB and was voted the National League rookie of the year in 2013, becoming one of the hottest pitchers in the sport.