The Forbidden Fist

Owen Deveris leads the Fairstead force that takes the city, and Jenna Wilder is the only person there who can meet him in a fight. He uses that. In exchange for the safety of the Wilder family he gets her to destroy her own power herself, and once she has, he goes after the house regardless and it falls. Jenna was born with strength nobody could explain and took to martial arts young, but women were not permitted to train, so she kept it hidden and let the city take her for ordinary. That was still the arrangement when the invaders arrived, which is why there was nobody else to put in front of Owen Deveris. Her master found her afterwards, repaired her meridians and brought her power back higher than it had been before, and she went back to the city.