The 17-year-old actress - who appeared as Walford's Ruby Allen - is to play young police woman Beth Green who is to be a series regular and will first appear on screen in May.
Of her new role, Louisa said: "I'm very excited to be going out on the beat."
An insider told The Sun: "Signing Louisa is a great coup as audiences really seem to like her. She’s going to be a full-time character and we’ve plenty of dramatic storylines for her to get involved with."
Louisa left EastEnders in November after being dropped from the show due to the lack of scope for her character. She subsequently appeared in Strictly Come Dancing, and was eliminated in the quarter final dance-off.