Welcome to Just Answer and thanks for your question. Your grandmother is listed in England and Wales Death Index, 1916-2005; Registration District Kensington, volume number 1a, page 112.. You can contact the authorities in Kensington for a copy or order one at the link below.
Her birth is listed in the England and Wales FreeBMD Birth Index, 1837-1915. Year 1869, 4th quarter, district name Newark, volume number 7b, page 298. You can contact authorities in Newark or order through the link below:
I have looked and looked and cannot find a marriage certificate for them.