You may have more information that is not in this thread but a few things haven't been clarified.
She had a half sister Mary Roberts and half brothers William and John Roberts. I have the family on the 1911 censusThe Roberts children in the 1911 census are Mary, James & Joseph-
www.census.nationalarchives.ie/pages/1911/Queen_s_Co_/Sallyford/Kilbrackan/791289John and William are the eldest of the 10 Roberts children that I found so far. Have possible marriage & child for John and possible death for William. Or did you mean James & Joseph (8th and 9th of the Roberts children).
Ellen's husband came to England (Stoke on Trent) in the 1950's, but came on his own and his death certificate doesn't state if he was single, widowed or divorced.It would be quite unusual to have marital status not on a certificate. Who was the informant?