The 22-year-old Dunkley put on 92 with Katherine Brunt, the biggest sixth-wicket partnership by England in ODI cricket.
Brunt added a crucial 33 从 46 as England overcame the loss of early wickets and some strong bowling from India to take a 6-2 lead in the multi-format series.
England had started their chase shakily in pursuit of a total that looked to be well below par on a good hybrid pitch, 但 Tammy Beaumont and Heather Knight fell early on for just 10 runs apiece.
But Dunkley, who made her ODI debut on Sunday, was able to hold her nerve despite her limited experience and dig in to see England over the line.
It took until the 11th over, with England already one wicket down, before Lauren Winfield-Hill opened up to score the first six of the match, but the Yorkshire batter edged behind just eight runs short of her 50 having looked assured at the crease.
Nat Sciver, who had become the fastest to 2,000 runs in terms of number of balls faced in the first ODI of the series, was dismissed for just 19, having been handed a reprieve by the third umpire who upheld a soft signal not out for a low catch, on just 13.
Amy Jones added a useful 28, while Dunkley, who had almost been run out early on after a poor call from the England wicketkeeper, brought up her maiden ODI half-century off 62 balls.
Earlier Kate Cross took five wickets for just 34 runs with India captain Mithali Raj again top-scoring for India, as they put on 221 after being put in to bat.
Having been labelled as a red-ball bowler, despite the lack of matches in the format, Cross claimed her second ODI five-fer on a hybrid pitch at Taunton.
Raj batted in similar fashion to the first ODI, making 59, but from a lengthy 92 deliveries as India struggled to impose a significant total after the loss of the opening pair.
Raj notched up her 14th ODI 50 in England, more than any other Indian player, male or female, but struggled to push the scoring on, with five of the batters failing to make double figures.
The dangerous teenage opener, Shafali Verma, was dropped by Lauren Winfield-Hill for 21, but the error was not too costly for England, after the 17-year-old only managed to add 23 more runs before being stumped by wicketkeeper Amy Jones with India 77 for two, having fallen just six runs short of her half century off just 55 deliveries.
Seam bowler Jhulan Goswami added a useful 19 from as many balls at the end of the innings to ensure India improved on their first-match total of 201.