Requiring just five points to break the Tigers' single-season point-scoring record, the star recruit crossed twice and slotted four conversions at Wagga Wagga's Geohex Park on Saturday.
McGregor's sparkling performance also helped the joint venture club claim their third victory of the season, meaning 2026 is their best season in terms of wins.
Cronulla picked up their fourth loss in five games as they struggled to complete their sets despite winger Georgia Ravics posting a double and centre Namoe Gesa scoring her first competition try.
Ravics drew first blood, but Wests hit back when McGregor dispatched a pinpoint kick to a soaring Emily Bass.
The Tigers' afternoon turned when lock Holli Wheeler was sin-binned after charging into the leg of halfback Chantay Kiria-Ratu, and Sharks prop Caitlan Johnston-Green capitalised.
But McGregor threw a dummy and scurried over to level scores at 10-all at the break.
Wests upped the ante in the second period, and were rewarded when McGregor danced across the line before the side ran in another three tries to two to complete the victory.
"What we needed at the Wests Tigers is somebody like that," captain Kezie Apps said.
"Just her (McGregor) as a player and how hard she's worked in the preseason and her leadership has been amazing."
Later on Saturday, North Queensland snapped their winless start to the season by producing an almighty comeback to beat Canberra 18-16.
After losing four consecutive matches to start their campaign, the Raiders crossed three consecutive times and looked on track to inflict further misery on their opponents.
But Cowboys winger Charlize Lloyd-Phillips was handed an eight-point try after she was hit high while scoring, before outside back Margot Vella stormed over twice to help North Queensland snatch the lead.
Canberra coughed up crucial last-minute errors, and the elated Cowboys celebrated their biggest-ever successful comeback.
The Sydney Roosters continued their unbeaten start to the season after centre Jess Sergis scored a hat-trick in a 38-8 thumping of St George Illawarra.
The Dragons were without their player of the year from last season Madison Mulhall after she ruptured her ACL, and the side continued to struggle in attack, registering under 10 points for a fifth consecutive match.
They did produce a spirited first-half performance, but tries to Sergis and second-rower Jasmin Strange on the stroke of halftime saw the Roosters balloon their lead to 14-4.
Winger Jayme Fressard extended the deficit in the 38th minute before interchange Tahlia O'Brien gave St George Illawarra a glimmer of hope by scoring her first NRLW try.
But Sergis and captain Isabelle Kelly took advantage of some timid Dragons defence to secure the Roosters' 23rd win from 24 games.
Five-eighth Jocelyn Kelleher also became the first competition player to notch 300 career points by nailing five conversions.
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