[6] Strallen appeared Off West End in the Menier Chocolate Factory production of Merrily We Roll Along as Meg Kincaid in 2013.
[8] Strallen played the role of Young Phyllis in Follies in the West End at the National Theatre from September 2017 to November 2017.
The Standard reviewer wrote: "The best news, by far, is Strallen, who exudes a lightness and brightness even when a mere face in the dance studio crowd early on.
Her acting and dancing is impeccable..."[11][12] Strallen starred in the title role in the West End revival of Mary Poppins, which premiered in autumn of 2019 at the Prince Edward Theatre.
[13] She had previously played the role of Mary Poppins in the UK and Ireland tour of the musical starting in October 2015.