She has been credited with songwriting work on commercially successful releases performed by artists including Sabrina Carpenter, Harry Styles, Justin Bieber, Selena Gomez, Tate McRae, Halsey, Rosé, and Shawn Mendes, among others.

[5] Allen began her career by working on a number of solo projects and formed Amy & The Engine, a four-piece indie pop rock group, before relocating to New York for a year.

Allen relocated to Los Angeles in November 2017, where she began collaborating with Scott Harris and eventually signed to Artist Publishing Group.

[3] Allen subsequently began writing and producing music with other singers, including Glades and JELLO.

[10] In 2019, Allen signed to Warner Records, and it was expected that her debut solo album would be released the following year.

[29] Allen co-wrote every track on Carpenter’s Short n' Sweet album which debuted at number 1 on the Billboard 200.

[31] In the same week, Allen claimed the number one spot on the Billboard Hot 100 Songwriters chart, with thirteen songwriting credits on the Billboard Hot 100 (including all twelve tracks from Sabrina Carpenter's number one album Short n' Sweet).

With this achievement, Allen became the sixth woman to reach number one on the Hot 100 Songwriters chart in the year 2024.

Allen is only the third woman in the history of the Hot 100 Songwriters chart to capture number one without also being billed as the recording artist.

[36] In a 2024 New York Times article, Allen also stated that she was inspired by the "'90s" girls - Sheryl Crow, Alanis Morissette, and Melissa Etheridge - as well as Cocteau Twins and Edie Brickell.