Chatham is in Harwick Township, Kent County
1851 census Howard Tsp, Kent County
James, farmer, b Nova Scotia, Methodist, 44
Jennette, b Scotland, Presbyterian, 40
Anne, servant, 18
Margaret, servant, 14
This census taken in 1852 and the ages given are the ones on the next birthday so Jane is likely 4, b around 1847/48.
She is the only Jane Brown of the right ages in the right area.
You can view this census on www.automatedgenealogy.com
Her marriage registration should have her parent's names on it. Also her death rego.