Kent left-arm seamer Natasha Farrant returns to the 15-strong party.
She replaces vice-captain Anya Shrubsole, who has been ruled out because of a side injury.
The series, which follows England's 3-0 victory in the one-day international series between the sides, begins at Bristol on Sunday.
England coach Mark Robinson said: "Sophie brings youth, vitality and another left-arm spin option."
Robinson added Beth Langston's absence with an ankle injury was a "real shame" and said seamer Kate Cross had been left out to undertake some "focused technical work".
England women squad: H Knight (capt), T Beaumont, K Brunt, S Ecclestone, G Elwiss, N Farrant, J Gunn, A Hartley, D Hazell, A Jones (wk), L Marsh, N Sciver, F Wilson, L Winfield, D Wyatt.
England women have named 17-year-old Lancashire left-arm spinner Sophie Ecclestone in the squad for the three-match Twenty20 series against Pakistan.