The Brisbane five-eighth won a tight selection battle to replace Sydney Roosters premiership winner Jocelyn Kelleher for Sunday's Women's World Cup final.
Kelleher started in three of Australia's four Cup games and was player of the match in the 40-0 win over Samoa on Test debut.
Southwell, who will partner Tarryn Aiken in the halves, filled her boots with 44 points of her own in the record-breaking 124-6 win over Wales.
Kelleher kicks goals too and shared a strong bond with Roosters teammate and halfback Aiken during their NRLW title win, but has been named in the 21 jersey for the clash with New Zealand.
"Tarryn and Jesse haven't played too much footy together, but I've been fortunate to play a lot with the both of them and watching them both link up is going to be pretty special," Australia and Brisbane fullback Upton said.
"The best thing about Jesse, and this goes unnoticed and without stats, is how much space she creates for the people outside of her.
"I've been fortunate enough to have that pretty much my whole career, and I'm excited for her to do that for Taryn and make her job a little bit easier.
"She's young, she's energetic, she's enthusiastic, she wants the ball and she wants to be a part of the game."
Australia cruised into the final four before receiving a welcome test in their comeback semi-final defeat of Fiji.
"The record-breaking games are probably not the best when you're prepping for finals footy, which is so different," Upton said.
"We've had the luxury of everything working out for us and that just doesn't happen when it comes to finals.
"So it was good to be under the pump."
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