Another name for Mary was Polly.2
Given the presence of four Timms children in Edmund Strong's 1850 household, query if they weren't younger siblings of Mary, which would make her maiden name Mary Timms.
Note the 1850 census shows she was born in Alabama, while subsequent censuses show she was born in Tennessee.
1 1850 Census, Lincoln County, Tennessee, Page 49-50 (Ancestry.com Image 98A and 98B of 438).
1860 Census, Lincoln County, Tennessee, Roll M653_1261, Page 21 (Ancestry.com Image 9 of 22).