Islacker began her senior career at FCR Duisburg in 2004,[2] where her team finished as Bundesliga runner-up twice in the 2004–05 and 2005–06 seasons. In 2006, she joined SGS Essen, then moved to Bayern Munich, achieving another runner-up finish in the 2008–09 season. She returned to FCR Duisburg in 2010 and later transferred to BV Cloppenburg in 2013.[3]
In July 2017, she returned to Bayern Munich,[5] and secured three consecutive runner-up finishes in the 2017–18, 2018–19 and 2019–20 seasons.
In 2020, she joined 1. FC Köln,[6] then moved to FC Viktoria Köln in 2023.[7] In January 2024, she signed with VfB Stuttgart.[8] At the conclusion of the 2024–25 season, with promotion to the 2. Bundesliga secured, Islacker announced she would be leaving the club to return to her native North Rhine-Westphalia for professional reasons.[9]
