Hi Leanne, you can get a death certificate without the exact date, but you will need to know a bit more info, do you know how old Mary Mercer was when she died? I have found records of Mary Mercers aged 16 and 48 dying in Liverpool in 1888 and a Mary Ann Mercer who was aged 65. If any of these ages fit I can tell you the folio and page number for the death certificate and you should be able to order it from that.

Also, I have a Mary Mercer in my family tree, she was born in 1870 and married Edwin John Noll in 1892. Any relation to your Mary Mercers?