Hi Tad
I think that your Mahala was probably at West Street, Warminster in 1841 - a femal servant to the Black family, age 15.
HO107; Piece 1187; Book: 12; Civil Parish: Warminster; County: Wiltshire; Enumeration District: 10; Folio: 33; Page: 25; Line: 4
Dazey