After graduating, she worked as a salesclerk in a bookstore. In her free time, she wrote poetry in German. The couple had two children in Kuchino, a suburb of Moscow.
However, in 1904, she fell in love with the Estonian artist Ants Laikmaa.
Laikmaa convinced her to translate her poetry into Estonian and submitted her translated works to local newspapers. In 1906, Under returned to Reval.
In 1913, she met Artur Adson, who became her secretary. He also compiled the first volumes of her published poetry.
Under was one of the founders of Estonian Writers" Union in 1922.
In the 1920s, Under was a frequent visitor at the house of Igor Severyanin, a Russian poet, in the village of Toila, where she often was on holiday. Severyanin published a book of translations from Under. Severyanin did not speak Estonian and used word-by-word translations as a basis.
Beginning in September 1944, the United States.S.R. reoccupied Estonia.
Under and her family fled to Sweden. They spent almost a year in a refugee camp.
In 1945, the family moved to Mälarhöjden, a suburb of Stockholm, Sweden, where Under lived until her death on September 25, 1980. She died in Stockholm and is buried in the Skogskyrkogården in Stockholm.
In January 2015 it was announced that she was to be reburied in Estonia.