I don't know if you have earlier census records but this looks like Mary's family in the 1891 census of Lincoln which shows her father as Owen KELLY, a 49 year old General Labourer, born in Ireland & her mother as Ann, aged 44, also born Ireland. Brother Patrick KELLY, who is lodging with William & Mary PARKINSON in the 1921 census, is also there aged 12 and born Worley, Kent. It might help you to narrow down which Mary KELLY born c1882 in Co Cork is your Mary KELLY. Again you may already have this information, but looking through the birth registrations of siblings Patrick & Margaret, their mother's maiden name is shown as MCGUIRE which may also help with finding Mary's baptism.
Janet