FindAGrave.com indicates that this is a relocation of her body from St. Anne's cemetery to Mt. Elliott. She is interred with her son, Barnaby, who died shortly after his mother. The FAG index states that she died in Jan. but the gravestone states July and the profile for her son supports that month also.
↑ "United States Census, 1850," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:MF85-RWM : 12 April 2016), Louisa Peters in household of * B Peters, Detroit, Wayne, Michigan, United States; citing family 1606, NARA microfilm publication M432 (Washington, D.C.: National Archives and Records Administration, n.d.).