Gilbert led 17-12 after the first quarter, 27-25 at the half and 40-38 after three.
The Lady Lions (17-4) were led by Crystal Lester's 20 points.
Britnee Gibson tallied 10, Kirstin Brown nine, Megan Thomas seven, Danielle Butcher five, Brittani Kirk two and Renae Cline one.
Montcalm (11-6) got 24 from Krislyn Bogart, 16 from Tara Havens and 10 from Lindsey Hamblin.
Gilbert made 14-of-18 from the free throw line. Montcalm was 6-of-7.