"We did what we could but the difference on the day was game time and we are quite a new side. Hopefully we can do better in the competition next year.
"Now we hope to go all the way in the league. If it isn't this year it will be in year's to come.
"We are a new side at the moment and the key to future success will be trying to progress as much as possible and help a lot of young girls here coming through."
Western Springs AFC, who are currently second in the NRFL, were leading 2-0 at half-time thanks to goals from O'Neill and Cooper - both right footed strikes in the box.
But the game was put out of reach after the break thanks to two coolly taken penalties from O'Neill, who slotted the first to the right side of the keeper and buried the second in the opposite corner, giving the keeper no chance.
Western Springs AFC manager Rico Wilson praised the striker's "stylish" hat trick and said his team will now be aiming to go all the way in the competition after being knocked out in semifinal stages last year.
"Rebecca playing up front had a great game and really stood out. She led the team well which was needed in such an important game," he said.
"There was a lot of pressure with the penalties especially, which she handled very well.
"I don't think we had a very good first 45 minutes but in the second half we had much better control of the ball in terms of our passing and tackling and just moved the ball a lot quicker.
"We were really disappointed with the way we exited the cup last year. We just didn't perform.
"But our intention is to go all the way this time. We are in it to try and win the cup."
United will look to bounce back in their next game in the WaiBOP Premier League when they face second placed Melville United at home.
It's a crucial game in the title race as currently third placed United are just one point behind their next opponents and top of the table Northern United.
And there is everything to play for as the new competition, which has seen the merger of Bay of Plenty and Waikato to make it a stronger division, will see the winning club go into a playoff match in a bid to qualify for the NRFL.
Manager Denise Smith said she hoped the cup experience would help the side ahead of their crucial fixture and is confident of a bright future for the club.
"We now focus on giving the title race our best shot and I want the players to use the positive cup run to their advantage."