In wet and cold conditions at Ikon Park on Saturday afternoon, the Blues led for the duration to prevail 9.6 (60) to 2.7 (19) in their first finals appearance since 2020.
Leading by just seven points at halftime, Carlton slammed through four goals in the first 10 minutes of the third term to stun the Eagles, who were in the club's first AFLW final.
McKay, the younger sister of Carlton captain Abbie and the daughter of club great Andrew, booted two of the third-quarter goals to inject serious energy into the Blues' team.
A contender for the AFLW Rising Star, the 19-year-old celebrated in style after slotting her important goals.
Fellow Blues young gun Poppy Scholz got in on the act, booting Carlton's fifth goal of the third quarter.
Mia Austin topped off a perfect term, kicking Carlton's sixth major after the three-quarter time siren.
The 21-year-old was mobbed by teammates after the goal and became emotional.
Austin has been dealing with the pain of losing her young cousin Ben, who tragically died after being struck by a ball at his local cricket club last week.
She didn't travel with Carlton to Perth when the Blues ended the home-and-away season last Friday night with a win over the Eagles.
"As a whole playing group, wider club, we've got around her as best we can and put in the supports we need," Carlton coach Matthew Buck said.
"It's a credit to Mia. She's been a real professional throughout and continued to train at a really high level.
"She's been out of the team for a number of weeks, but she's been training well and took her opportunity with both hands.
"She took her moment as well which I was really proud to see."
Irishwoman Erone Fitzpatrick got Carlton going, producing a classy finish on the run, and went to the main break as the game's leading disposal winner with 14.
West Coast failed to score in the first quarter, but hit back hard in the second term, mainly thanks to young superstar Ella Roberts.
The midfielder pounced on a loose ball, effortlessly snapping through the Eagles' first goal.
But it was all Carlton from there as Dayna Finn and Fitzpatrick joined Sophie McKay in being a multiple goal-kicker.
Lucia Painter, who appeared to have badly hurt her knee in the first quarter, kicked West Coast's second goal of the match during the last quarter.
West Coast farewelled dual All-Australian Dana Hooker, who retires from the AFLW after 67 games.
"The biggest thing is that belief that we made it to finals," Eagles coach Daisy Pearce said.
"We've just got to double down on it now."
The Blues will meet Hawthorn next week in a semi-final.
After going goal-less in their qualifying final against rampaging North Melbourne on Friday night, the Hawks will need to recover while dealing with a host of injuries to key players.
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