Estelle joins United from Paris Saint-Germain, where she spent the previous two seasons, following periods with Bordeaux, Paris FC and Olympique Lyon – winning two Division 1 titles and two French Cups in her career.
Estelle made her full international debut for France in 2017, in a friendly against Ghana, after representing her country at all age groups from under-16 upwards.
Cascarino said: “I am so happy and excited to be here. I want to grow as a player and a person, and help the team win trophies.
"On the pitch I am a fighter and like to help the team in both attack and defence.