England women had won the first ODI by eight wickets.
India, who were all out for 221 in 50 overs after being put into bat, began well by reducing England to 92 for four. They managed to remove the stars of the first match Tammy Beaumont (10) and Natalie Sciver (19) early.
However, Sophia powered them to the target, hitting five fours and a six as the Indian bowlers struggled to get rid of her.
Earlier, England pace bowler Kate Cross took five wickets for 34 runs to help bowl Indian women out for 221.
Indian skipper Mithali Raj scored a half-century before developing neck pain.
The visitors had got off to a flying start with openers Smriti Mandhana (22) and Shafali Verma (44) adding 56 before a loss of three quick wickets, including the close stumping of Shafali, put them on the back-foot at 77 for three.
Harmanpreet Kaur (19) and Mithali (59 off 92 balls) then added 68 runs for the fourth wicket before Harmanpreet fell. As wickets kept tumbling around her, Mithali remained the lone batter standing.
Towards the end, Jhulan Goswami (19) and Poonam Yadav (10) added 28 for the last wicket to take India past 200.
Left-arm spinner Sophie Ecclestone took three wickets for 33.
Brief scores: India Women 221 all out in 50 overs (Mithali Raj 59, Shafali Verma 44, Kate Cross 5/34, S Eccleston 3/33) lost to England Women 225/5 in 47.3 overs (Sophia Dunkley 73 not out, Katherine Brunt 33 not out, Lauren Winfield Hill 42, Poonam Yadav 2/63)