Australia, who were knocked out in the round of 16 at the 2019 World Cup, are coming in on the back of a 1-0 win against one of the major contenders, France.
The Matildas have won seven of their last eight matches and emerged as genuine contenders from a bleak period, having never passed the World Cup quarter-finals stage.
France is probably the third team in the top 10 that Australia have beaten in the last couple of months, Arnold, who has been selected for her third World Cup, told reporters after training in Brisbane on Sunday.
"To get results against those teams and a couple clean sheets as well, I think it shows a lot of confidence and consistency," she said. "So yeah, a lot of confidence heading into the first games."
Arnold said their mindset would remain the same when they kick off their Group B campaign on Thursday against Ireland in Sydney before playing Nigeria and Canada.
"I think as long as we just stick to our game plan, we take (it) game by game, I think that's probably the most crucial for us to be doing to start this World Cup," she added.
More than 80,000 people are expected at Sydney's Stadium Australia for their World Cup opener, and the West Ham keeper said the support from fans has been incredible so far.
"It's starting to feel a little bit more real now," Arnold said.
