Mary Ann is recorded as baptised on November 16th 1856, in Charlwood, the address of her mothers parents and family.
Having found no other reference to her, and finding her missing from the 1861 census, where her sisters Ellen and Clara are recorded, it is perhaps most likely she died in the first 5 years of her life.
Her parents married on 30th March 1856, and presumably she was born a little time before her christening. It is possible her mother knew she was expecting when she married; her parents seemed to move twice before the 1861 census. Her sisters are recorded as being born in Chilham (East Ashford); in 1861 the family lived in Westerham.
It is possible that Mary Ann was looked after elsewhere, but she was not at her grandparents (who had young children themselves.).