Rosé is from the city of Lior in a remote region of the East. She was a devout follower of Cornello's teachings because she felt that he would use his powers to bring her boyfriend, Kain, back to life. Instead, Cornello created a talking parrot chimera to mimic Kain's voice. When Rosé discovered this, he locked her in the room with it, using the incomplete Philosopher's Stone to get it to attack her. Al saved her, and together with Ed, they discredited Cornello.
In the 2003 anime:
After Cornello's plan had been exposed and with her hope shattered, Rosé was forced to start over and persevere through hard times when the military intervened in Lior. Rosé was imprisoned by the military. When she is next shown, she is free and has a child. It is unknown how she got it, though it is implied that she was raped while in military custody. Scar uses her as the symbol of hope for the people of Lior, referred to as the Holy Mother. Later, seeing Edward paralyzed at the sight of Sloth, Rosé gets her voice back and uses what he told her before to snap him out of it. She became targeted as Dante's next vessel with the new Philosopher's Stone. Dante hypnotized Rosé, and her baby was used by Dante to open the Gate. While she's kept with Dante in the underground city, Edward finds her dancing alone in the ballroom under the trance. While the two of them are dancing, Rose tells Edward that she had been waiting for him. She then tells Ed that she loves him. Edward blushes and pushes her away, asking if she knows what she's saying and that they're "just friends". It is unclear if Rose said it under Dante's "hypnosis" or genuinely loves him. (In the Japanese dialogue, Rosé doesn't tell Ed that she loves him. Although, it is somewhat implied she might say it and Edward pushes her away and asks if Al was brought there.)
Edward's death breaks her trance. At the end of the anime, Rosé and her child appear to have moved to Risembool, living happily with Winry and Pinako.
In the 2009 anime:
Taking Ed's words to heart, she helps to rebuild the town, eventually reuniting with Alphonse Elric. She makes a comment on how she is depressed that Ed is not with them, admitting that she has really missed him and that she wishes to see him again. This causes Winry to become slightly jealous, something Al catches and taunts her with.
She later comments to Winry how she is thankful toward Ed for opening her eyes to the false belief and got the town moving on their accord.