But they got away with it as Georgia Wareham (2 for 11 from three overs) and Megan Schutt (2 for 13 from 3.4) joined Gardner in ripping through the English.
"We did not have our best day in the field. But the bowlers did a good job," Lanning said after the victory.
Australia bounced back from a loss to India in group play to record big wins in the two knockout games. Lanning said their final defeat two years ago to the West Indies and a semifinal exit at last year's 50-over World Cup were key motivators before yesterday's final.
"The last two World Cups really hurt and we had to change a few things and move it forward. The group embraced it and it was a very satisfying win. The loss against India did not rock us - maybe a couple of years before it would have rocked us - but we were very calm," Lanning added.
Australian wicketkeeper Alyssa Healy was named player of the tournament.
"It's pretty special and we've worked hard in the last 12 months. Win or less today, we're proud of the way we played," Healy said.