Did you see on the 1891 census there is an older daughter - Emily C Allen 19, but that would make her 9 in 1881, the same age as Mary is given. However on the baptism, Mary is born 1876, so she'd be 5 in 1881 not 9! Has to be the same family, perhaps they weren't any good with dates. Where is Emily in 1881 as well?