Wilhelmine was born in Vienna as the third of four children of Moriz and Amalia Brill. After studying medicine at the University of Vienna, where she graduated in 1914, Wilhelmine worked as a pediatrician. In September 1913, she resigned from the Jewish Community (IKG) on the occasion of her engagement to the doctor Ernst Löwenstein. The couple's civil marriage took place in Vienna on 9 October 1913. The family lived with their three children Hans Georg (1914), Karl Otto (1916) and Erika (1919), first in Vienna’s 9th district, at Maximilianplatz 15/5, today's Rooseveltplatz, and later in a house Wilhelmine bought at Bastiengasse 61 in Vienna’s 19th district, in 1916. Wilhelmine Löwenstein continued to practise her profession after marrying and starting a family. She worked in Clemens (von) Pirquet's children's clinic, which was established in 1911, and specialized in the treatment of tuberculosis in children, as did her husband, who had since habilitated at the University of Vienna. In the interwar period, Wilhelmine Löwenstein was involved in the women's rights movement; in 1928, together with Marianne Beth, she founded the Austrian Association of Working Women and was president of this association for a time. In 1929, she was a founding member of the Vienna Soroptimist Women's Club and served as its president. Both associations were dissolved after the annexation of Austria to the German Reich in 1938.

From March 1938, Wilhelmine and Ernst Löwenstein were among those persecuted. The revocation of their venia legendi (permission to lecture) was followed by Ernst Löwenstein's dismissal on 22 April 1938. Their two sons Hans and Karl, who had studied medicine like their parents, lost their positions at the University of Vienna in April 1938. Hans fled to the USA via Liverpool in June 1938, Karl followed in December 1938. Daughter Erika, who had been married to Michael Robin A. Chance, a well-known ethologist and pharmacologist, since 1937, was already living in London, where Wilhelmine and Ernst Löwenstein also fled to in July 1938. In her declaration of assets dated 8 July 1938, she listed real estate, including the “industrial palace” she had inherited together with her siblings, a car that had been seized by the police, a number of shares as well as the practice and home furnishings with furniture, Persian carpets, porcelain and works of art, which she identified as her daughter's marital property. The “Industrial Palace” was “aryanized” in autumn 1938 and subsequently used as the “House of the Army” by various branches of the Wehrmacht.

Wilhelmine and Ernst Löwenstein arrived in the USA with an NQIV visa (non-quota immigrant visa) at the beginning of August 1938. They settled in San Francisco, California, where Ernst took up a position at the Hooper Foundation of the University of California and Wilhelmine Löwenstein began working as a general practitioner. Her belongings were confiscated in November 1940 and sold or auctioned off by Vugesta. In 1947, the properties seized from her were restituted. In 1955, the “Industrial Palace” was returned to the Brill siblings or their heirs. Wilhelmine Löwenstein died on 1 August 1971 as the result of an accident in San Francisco.