McGill advanced to play the No. 2 Western Mustangs in Sunday's final after Western blanked the No. 6 Montreal Carabins 2-0 in Saturday's late semi. St. FX will play Montreal for bronze.
Davidson fired a Leslie Oles rebound into the net past X-Women goaltender Sojung Shin with 48 seconds left on the clock.
"I saw my teammate walk in the slot and I figured I would go sneak back door and I was fortunate to get the puck on my stick and bury it," Davidson said. "We believed in ourselves, we just kept going and we knew it was going to come eventually. We knew that we were going to get a goal one way or another."
Taylor Hough stopped 11 shots for the shutout. Shin made 36 saves in the losing effort.
McGill came out flying in the first period, testing Shin early and often. The X-Women escaped the first period with a scoreless tie, despite being outshot 13-5. With more of the same in the second, the Martlets kept pressing and Shin continued to shut them down, including a huge save on a breakaway attempt by McGill captain, Katia Clement-Heydra.
The X-Women threatened early in the third with a few close calls, but Hough was able to keep the puck out.
"What we really focused on was playing D," said X-Women coach Ben Berthiaume. "We knew they were an offensive style team that's really quick, so we wanted to play a good defensive game and try to keep them to the outside as much as we could and we knew if we kept them to the outside Sojung Shin would take care of the perimeter shots which she did."
In the late game, Kelly Campbell made 28 saves as Western shutout the Carabins to earn a spot in Sunday's final.
Cassidy Gosling put the Mustangs on the board 19:40 into the second period and Kendra Broad added an empty-net goal with 28 seconds to play.
"Today there's no question that Kelly Campbell won that game for us," said Western head coach Chris Higgins. "We battled, in the last five-six minutes I don't think they got any scoring chances, but boy was she good."
Earlier, Moncton downed Alberta 4-1 in the fifth-place game.