[2] At age 17, Rainsford first acted, in Macbeth, in Grand Central Station, in New York, for Prince Andrew and Mayor Giuliani.
[3][5] In May 2013, Rainsford appeared in The Seagull at Oxford Playhouse via Nuffield Theatre, Southampton and Headlong, touring UK to 22 June 2013.
[6][7][8][9][10][11][12][13][14][15][16][17] In May 2014, Rainsford appeared as Mrs. Fanny Wilton in Henrik Ibsen's John Gabriel Borkman for BBC Radio 4 Extra.
[19][20][21][22] As well as her role as ”Boo”, while seven months pregnant,[2] in the television series Fleabag,[23] Rainsford's television credits include Finding Joy, The Smoke, Law and Order UK and Da Vinci's Demons.
[27][28][29] In February 2019, Rainsford starred in Sir F. Mother Fucking Drake, Bea Roberts' filmed monologue about growing up in the shadow of Sir Francis Drake as a young woman, a wry pitch-black comedic nod to English imperial history, for the Young Vic Theatre.