Hello,
I think I have found the burial place of Mary Ellen Roberts (nee Aston) and her husband William Roberts in Toxteth Park.
There are the following Aston/Roberts graves in Toxteth Park Cemetery:
In Consecrated Section D, Grave 116 are:
ASTON George, 34 years, Book Keeper, Finch Street, 12 October 1857
ASTON Samuel, 55 years, H.M Customs

, 40 Crown Street, 19 July 1868
ROBERTS Emma, 7 years, Infant, 40 Crown Street, 10 December 1869
ROBERTS Mary Ellen, 69 years, Married Woman, The Town Hall Birkenhead, 28 April 1914
ROBERTS, William, 74 years, -, 22 Truro Road Wavertree, 30 November 1916
In Consecrated Section D, Grave 274 are:
ASTON Edward, 29 years, Collector, 44 Crown Street, 12 April 1872
JONES William Henry, 23 years, Joiner, Mill Road Hospital Everton, 4 June 1877
ROBERTS Mary, 68 years, Widow, 14 Cambridge Street, 20 May 1878
It looks therefore like Mary Ellen Aston remained married to William Roberts up to her death in 1914.
Alison xx