I think you are right about her being unmarried.
It must be frustrating for you with the person who did the blog on the family failing to respond to your request.
I think it might be worth looking at Mary Evans' death and her Will, if any. That might give some clues about Hannah Grace. I think Mary Evans is still in Dwygyfylchi in 1891. She is Postmistress at Bryn Aber and with son, Richard age 30, General Labourer, born Penmaenmawr. Grandson, Thomas, age 11, born Penmaenmawr. Thomas is presumably the son of Hannah Grace as he was with Mary in the 1881 census age 18 months.
I have looked at the address in 1891 and it seems to be around the same area as in the 1881. Have you tried a place search of Dwygyfylchi to see if she is there after that? Mary Evans is shown as aged 65 in 1891. It is going to be a tough task to find a death for Mary Evans without more information.
Jo.