While there are some beach scenes, Winry is typically seen in her usual attire: her mechanic overalls. This is consistent with her personality and role in the series - she's a skilled mechanic and her focus is on her work.
It's worth noting that while not featured in *Brotherhood*, a swimsuit design for Winry was created for the *Fullmetal Alchemist* video game, "Fullmetal Alchemist: The Sacred Star of Milos."