With Ikast-Brande (later FC Midtjylland) she won several trophies, including the 2015 Danish League.

She won the Bundesliga twice in 2022 and 2023 and the 2021–22 Women's EHF European League.

In the summer of 2023 she switched to Romanian top club CSM București.

Østergaard debuted for the Danish national team in 2011 against Russia.

She made her first major international tournament at the 2013 World Women's Handball Championship, where she played the most minutes of any Danish player.