This is a turn-of-the-century dress with a pouter pigeon bodice, shallow vee waistline, and complex sleeves supporting Wikimedia's date of ca. 1900. I cannot resolve what the vertical band and associated bands are in the middle of her skirt.
Keywords: Kühn, Marie Louise of Hanover, Prinzessin von Hannover und Cumberland, Prinzessin Maximilian von Baden, Princess, Duchess, Welf family, Baden family, German, bouffant coiffure, ribboned hat, pouter pigeon bodice, high enclosing neckline, collar, pin, lace bertha, quarter length puffed upper sleeves, elbow length flared middle sleeves, long close lower sleeves, cuffs, waist and, shallow vee waistline, close maxi-length skirt, gloves, shoes, umbrella