Mid 18th century; earliest use found in Robert Forbes (bap. 1708, d. 1775), Jacobite annalist and Scottish Episcopal bishop of Ross and Caithness. From lucky + minnie.
Definition of lucky minnie in US English:
lucky minnie
nounˈlʌkɪ ˌmɪni
Shetland, Orkney, Scottish rare
One's grandmother; a grandmother.
Origin
Mid 18th century; earliest use found in Robert Forbes (bap. 1708, d. 1775), Jacobite annalist and Scottish Episcopal bishop of Ross and Caithness. From lucky + minnie.