with her local Women's Big Bash League (WBBL) team, the Brisbane Heat, as a marquee player for the competition's inaugural season. She took the fourth-most wickets during the 2016–17 season (18 at an average of 15.88), before the Heat were knocked out of the tournament via a crushing nine-wicket semi-final loss to the Perth Scorchers at the WACA. Two seasons later, Jonassen was at the centre of an iconic moment during the first WBBL|04 semi-final at Drummoyne Oval against the Sydney Thunder, bowling the final delivery of the match to Nicola Carey who initially appeared to hit the ball for a game-winning six until an unlikely catch by Haidee Birkett was taken metres inside the boundary rope. On the following weekend in the final against the Sydney Sixers, Jonassen contributed 1/28 from four overs as the Heat went on to win by three wickets to claim their maiden championship. Jonassen enjoyed an outstanding WBBL|05 campaign, notably increasing her output with the bat (scoring 419 runs at an average of 38.09) for which she credited an "honest conversation" with new coach Ashley Noffke. She also took the second-most wickets in the league with 22 at an average of 18.31 and won the Heat's Most Valuable Player award. In a four-wicket semi-final win over the Melbourne Renegades at Allan Border Field, Jonassen earned Player of the Match honours by taking 1/25 and scoring 38 off 23 balls. The following day, in the final against the Adelaide Strikers, she finished with match best bowling figures of 2/30 and contributed 33 runs. The Heat won by six wickets, thus becoming back-to-back champions. In July 2020, Jonassen signed a new contract to stay at Brisbane for another three years. The Heat also announced she would captain the team for WBBL|06. International career 2012: Limited overs debut, first world championship Jonassen made her international cricket debut in a Twenty20 match on 20 January 2012 against New Zealand at North Sydney Oval. She took two wickets for 28 runs from four overs, with her first scalp being Suzie Bates who was caught by Lisa Sthalekar for 33. In the second innings, Jonassen scored eight not out and put on an unbeaten 25-run partnership with Sarah Coyte to help Australia win by four wickets with one ball remaining. On 25 January 2012, Jonassen made her One Day International debut at the Sydney Cricket Ground against New Zealand in