She plays on the Ladies European Tour and won the 2023 KPMG Women's Irish Open.

[3] She lost the final of the 2019 Danish National Match Play Championship to Cecilie Finne-Ipsen,[4] and in 2021 she finished runner-up at the Danish National Stroke Play Championship, one stroke behind Nicole Bonde Lorup.

[5] Sønderby finished 3rd at the 2020 Portuguese International Ladies Amateur Championship, behind Alessia Nobilio and Carolina López-Chacarra.

[8] Sønderby quit university after one season and turned professional, after securing a place on the 2022 Ladies European Tour in Q-School at La Manga Club in December 2021.

[14] In September 2023, she earned her first win on the Ladies European Tour at the KPMG Women's Irish Open.