“When you get married put ha’pennies in your shoes. My great grandmother told my mother that, and my mother told me. My mother is only around .02% Irish, but my great grandmother was “off the boat” Irish and immigrated here illegally. She even had to change her name.”
Ha’pennies are British halfpennies worth 1/480th of a pound sterling, and was discontinued by the British government in 1969, so Emily’s grandmother’s story must originate before then. Perhaps Emily’s grandmother got it from the Victorian rhyme, “something old, something new, something borrowed, something blue, and a silver sixpence in your shoe,” and simply changed penny to ha’penny (1). There also exists an Irish version of this rhyme (which stays mostly the same) wherein the Irish penny in your shoe would guarantee the good fortune of the newly married couple.
Sources:
(1) http://www.weddings.co.uk/info/tradsup.htm