This is the only Margaret born in Stirlingshire (in the BVRs) with a father John and a mother Helen
CAMPBELL, Margaret Gender: Female Christening Date: 1 Jan 1751 Recorded in: Falkirk, Stirlingshire, Scotland Father: John CAMPBELL Mother: Helen MONTEITH Source: FHL Film 1041943 Dates: 1743 - 1819
There are another two Margaret Campbells but the parents names don't match up with yours, they are:
CAMPBELL, Margaret Gender: Female Christening Date: 18 Mar 1785 Recorded in: Falkirk, Stirlingshire, Scotland Father: Alexander CAMPBELL Mother: Janet CAMPBELL Source: FHL Film 1041943 Dates: 1783 - 1839
CAMPBLE, Margaret Gender: Female Birth Date:n 12 Apr 1785 Christening Date: 17 Apr 1785 Recorded in: Stirling, Stirlingshire, Scotland Collection: St John Street; Associate Session Congregation Father: Archibald CAMPBLE Mother: Elizabeth RUSSALL Source: FHL Film 889487 Dates: 1738 - 1816