What happened to Georgiana Owen?

[LizzieL]

Thanks, you beat me to it, I was laboriously going through 1861 census for Rosinas born in right area.
That explains why her birth was indexed  in both surnames by GRO.

[Sloe Gin]

I believe there are cases of illegitimate birth registration where the father is present to acknowledge the child, and so the child bears the father's surname, but no maiden name is recorded for the mother as she had not changed her name.

But the mother would still have a maiden name.

Not so.  "Maiden name" is often assumed to be the same as birth name.  But the "maiden name" is the surname used by a woman at the time of her first marriage.  So she doesn't have a maiden name unless and until she marries, and it won't necessarily be her birth name when she does.