Caroline is the proper and original spelling.
I abhor those parents who think they'll make their little darling different by spelling their names in a 'unique' way.
All they do is condemn the poor soul to a lifetime of explanations, and mis-spelling.
The Scots Gaels have this weird habit of christening some girls Johann, and pronouncing it Joan. Every time I see it, I think, not of a contraction of Johanna, but as the christian name of a great composer.