Harden and PNG centre Long will put their partnership to one side when they face each other in York on Monday (Tuesday AEDT) with a chance to make it to the final on the line.
Long, a bank teller by day, and speech pathologist Harden have played against each other before, but now get the chance to do it on the world stage.
"It's a pretty big occasion to play against your partner in a World Cup match," Harden told AAP.
"It'll definitely be one to tell the family about. We are pretty good at separating footy and our life away from it.
"We are dachshund mums to Percy and Gordon. We're both really excited for the game and are passionate about playing for our countries, but there are no friends on the field."
Bookmakers have Australia priced at 1-500 to win against PNG, with a final between the winner of the other semi-final between New Zealand and England beckoning for Brad Donald's side.
After winning their opening two group games over France and the Cook Islands by a combined scoreline of 166-0, Australia were given a run for their money in their final pool fixture against New Zealand.
While they survived to eke out a 10-8 win, Harden - who will play at prop against the Orchids - said the tune-up will stand them in good stead as they seek to claim a third straight title.
"We came in just wanting to improve with each game, we wanted to trial a few things in the pool stages," she said.
"The game with New Zealand seemed really physical from the sideline and the speed was really high.
"It's been a really good process for us to have New Zealand in our pool because you want to test yourself out against the best.
"It's all about the semi final now and PNG are going to be very physical too."
