"It has to be our greatest achievement and the club's best-ever season," said Karen, manager since 2009.
dramatic late winner secured the highest cup accolade the team can win at their level - the FA Cup usually won by Women's Super League teams - as the FAWPL's North and South divisions come together for the 'national cup'.
Bianca Baptiste opened the scoring at Kidderminster, Cardiff levelled on the stroke of half-time and it stayed that way until Vio rose highest to head home Ronnell Humes' cross in the final minute of extra time.
It meant the team lifted a second trophy to add to the Ryman Cup in a season where they've finished sixth in the FAWPL and reached three cups finals.
Below: Karen with goalscorer Maya Vio and goalkeeper Toni-Anne Wayne after the final whistle
Karen feels this campaign now tops 2014-15, where they finished a best-ever fifth in the FAWPL, matched their best run in the FA Cup (fifth round) and lost the Ryman Cup Final.
"To have won two trophies including the national cup and still finish sixth has to be our best-ever season," she said.
"It has been a special season with a special group of players. We set out from day one to bring silverware back to the club, especially after missing out last year, and they delivered.
"Even better, they picked themselves up after losing the Capital Cup to put in a performance like they managed on Sunday.
"The players were a bit deflated to go in 1-1 at half-time but they dug in and I felt there was only going to be one winner once we got into extra time.
"The emotions all came out when Maya scored that winner. We all went crazy because we knew that was time up. They were great scenes.
"It just shows how far we've come - and we all believe we can keep improving. Roll on next season!"