Early results indicate the party failed to secure a lower house seat despite intense campaigning.
But it did secure at least one upper house seat, which was the objective of the preference deal, with state leader Colin Tincknell claiming the South West.
Mr Tincknell said the party had a good chance of winning another upper house seat in the Mining and Pastoral region with candidate Robin Scott.
There would still be some soul-searching during the election debrief, Senator Hanson said.
"Doing the deal with the Libs has done damage to us, in all honesty. It was a mistake," she said.
"We are really going to have to have a good look at this because all I heard all day leading up to this election was 'why are you sending your preferences to the Liberal party?'
"It wasn't One Nation. I think it was Colin Barnett - people did not want Colin Barnett."
She said the two-term Liberal leader should have stepped aside or been given the boot before the election.
"It's like when you've got milk in your fridge and it's starting to go sour, you throw it out, and that's what they should have done."
She also admitted the campaign started late, didn't have a big party machine behind it, and candidates were inexperienced.
But she still believed the result was good.
"You can't deny that we've done extremely well here - there is a place for One Nation in Western Australia so it can only grow from here," she said.
"Major parties, have no doubt, they see me and One Nation as a threat to their political existence."
She labelled the victors Labor "liars cheats and hypocrites" who could not be trusted for placing the Liberals above One Nation on how-to-vote cards.
"If we win seats in the upper house, we can keep the Labor party, hopefully, honest."
Senator Hanson told her party function in Perth's southern suburbs that she never expected to win lower house seats, despite telling reporters when she touched down on Sunday that the party had a chance to win the seats of Pilbara and Kalgoorlie.
Mr Tincknell chipped in to nominate Albany, Baldivis, Darling Range and Swan Hills.
Agriculture Minister Barnaby Joyce said the One Nation result was "a bit of a shocker".
"It hasn't been a good day in the office. Questions need to be asked on what that was about," he told the ABC.
