The side - still only in their first full season together - made it an incredible 41 wins from 41 matches as they lifted the silverware at the SecureCloud-sponsored event at RAF Halton in Buckinghamshire.
“I sometimes have to pinch myself to check I’m not dreaming,” said team manager Simon Potter. “This is such a very special group of players. 41 games without defeat and this prestigious trophy in the cabinet - it’s beyond our wildest dreams!”
The Borough girls reached the final without conceding a try in their five group matches and then faced a very strong Reading & Newbury team in the showdown.
They won that 25-5 to clinch the title.
Peterborough United linked with Ben Garrity as Port Vale boss seeks to play down link
Darren Ferguson says Peterborough United lacked the ambition to stay in the Championship and he's staying patient while waiting for the right job opportunity to come along
Supercomputer predicts likely outcome for Plymouth Argyle v Peterborough United, Derby County v Barnsley, Sheffield Wednesday v Charlton Athletic, Bristol Rovers v Oxford United and every other League One fixture
Peterborough United live blog: Posh face Plymouth for the second time in four days- this time in League One
Strong EFL Cup performance has given Peterborough United boss Grant McCann decisions to make ahead of Plymouth rematch
“All the hard work is paying off,” added coach Paddy Murray. “I can’t praise these girls enough. The effort, the desire to win, the brilliant team spirit, all of it is second to none, and they really deserve the success.”
England ladies internationals Claire Allan and Megan Jones arrived by helicopter to watch the event, just a day after thrashing Scotland 64-0 to make it four wins out of four in the Six Nations, and they spent time chatting with the Peterborough girls.