MARY MARR emigrated to London late nineteenth century from , I think, Cork or Clare.I do not know any more.
Hi Richard
There are 4 birth/baptism records of Mary Marr on www.rootsireland.ie/
1836 Wexford 1872 Laois 1892 Antrim & 1899 Meath (Mary Jane)
I assume that if she travelled late 1800's then only the firs 2 could be your Mary.
Do you have her age from a census record?
Col