Mary Kelly's child

There can only be one person. Thinking aloud really...
It doesn't fit with the story I'd conjured.
I'll check this again, and probably again. Then some more.
'Mary Kelly' wasn't called Mary Kelly and she wasn't ruddy Irish, but she knew the family. Came from the same village.
But why call herself a member of the Kelly family?
So she wasn't a catholic ... Least her son wasn't, unless he followed his father's denomination.