The female equivalent of a lounge suit is a smart or cocktail dress, trouser suit, or skirt and jacket. The length of the dress or skirt should be at or just below the knee.
Going to an event that has a lounge suit dress code requires dressing a bit more dressier than an event with a cocktail dress code but not as formal as a morning dress event. Popular materials for the dress are satin, silk and chiffon. The dress or suit is accompanied by formal shoes and jewelry. If the event is outside during the summer, a hat is appropriate.