The Magpies are without Brianna Davey (ACL) for the season while Steph Chiocci (achilles) was a late withdrawal but Collingwood still proved too good to win 6.5 (41) to 2.2 (14) at Victoria Park on Saturday.
Bonnici racked up 26 disposals, 11 contested possessions, six clearances and 10 tackles to inspire the Magpies, as one of three stand-in co-captains alongside defenders Stacey Livingstone and Ruby Schleicher.
She was well supported by Jaimee Lambert (25 disposals, six clearances) and Sarah Rowe (18 touches), while Aisling Sheridan booted two goals.
"Britt's reliable, she's taking her game to another level week-in, week out. She's a really good competitor," coach Steve Symonds said.
"Jaimee Lambert's another competitor in there and the two of them really get their hands on the ball and give us great drive
"The solution is how much time we spend with them together in there, how much time we balance that up. We'll work that out as we go along."
While the Saints were kept goalless for the opening three quarters, Olivia Vesely (15 touches) was solid through the midfield while Cat Phillips was also busy.
Both teams were affected by COVID-19 related absences.
St Kilda were without coach Nick Dal Santo, with Paddy Hill deputising.
Collingwood star forward Chloe Molloy and St Kilda's Rhi Watt also both missed out through the league's health and safety protocols.
The Magpies seized full control by the first break, snatching a 21-point lead.
The Saints were far more competitive in the second term but only added a point to their tally.
Sheridan struck in the second and third quarters to all but put the result beyond doubt, while Mikala Cann's snap early in the fourth gave Collingwood a game-high 39-point lead.
The Saints finally drew blood when Molly McDonald thumped a powerful left-footed effort home midway through the final term.
In the final minute Kate Shierlaw, on her return from COVID-19, grabbed a big mark and converted to keep the scoreline respectable.
Stand-in coach Hill was happy with how his team responded after a rough first quarter.
"Part of maturing as a team is to understand what your roles are and how you need to play them and not get too caught up in what's going on on the scoreboard and just get back to process," he said.
"I thought they did it really well after quarter-time."
Collingwood are now two wins from two and top of the ladder while the Saints are still hunting their first victory.
