Hi Greg,
I have been all through the 1851 census and can't find your Selina Calligan. I tried all Selinas born 1846 +/-2years in Birmingham...but no luck.
I also looked for ANY Calligans in Birmingham and only came up with one who could possibly be Selina's father...a Jeremiah Calligan, born in Ireland..wife Bridget...living on Weaman St, Birmingham.
As Hackstable says, you will need to get her birth cert ..that will unravel the mystery!
Cheers,
India