Milling supported the UK remaining within the European Union in the 2016 UK EU membership referendum. After the referendum, she helped to organise Boris Johnson's 2016 Conservative leadership campaign. In the 2017 general election, she was re-elected with an increased majority of 8,391 (17.6%). She was made an assistant government whip during the reshuffle on 9 January 2018. Milling voted for then Prime Minister Theresa May's Brexit withdrawal agreement in early 2019.